When comparing Transmission vs CleanMyMac X, the Slant community recommends Transmission for most people. In the question“What are the best Mac OSX apps for someone that's new to Apple?” Transmission is ranked 4th while CleanMyMac X is ranked 17th. The most important reason people chose Transmission is:
Transmission is free, ad-less and open source software licensed under GPL with parts under MIT with source code available [here](https://trac.transmissionbt.com/browser/trunk). Being open source allows anyone to check if the software has no malicious code, is secure and respects privacy.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Free, ad-less and open source
Transmission is free, ad-less and open source software licensed under GPL with parts under MIT with source code available here. Being open source allows anyone to check if the software has no malicious code, is secure and respects privacy.
Pro Very minimalistic, straightforward design philosophy
Transmission is great for getting things done without looking too much under the hood. It still has advanced options, they're just tucked away from sight.
Pro Very lightweight
Transmission-gtk uses only 17 mb of RAM in idle state and 24 mb in download state.
Pro Native Mac, GTK+ and Qt interfaces provide seamless integration with OSX and Linux systems
Transmission works well on OSX and various distributions of Linux due to having interfaces natively developed for those operating systems instead of haphazardly ported.
The Mac interface is written in Objective-C, uses dock badges and Growl notifications while the GTK+ interface follows GNOME Human Interface Guidelines and has support for popup notifications, desktop sounds, and a system tray.
There's also an unofficial port of Transmission-Qt for Windows.
Pro Full-featured
Transmission covers basics such as Prioritization, Selective Downloading, DHT, PEX, LPD and Magnet URIs. It has graphical, web and command line interfaces. It includes MSE/PE for security. Has UPnP, NAT-PMP, NAT traversal for automatic router configuration. Has UDP tracker and µTP data transfer protocol support. Even covers IPv6, Web seeding and Local Peer Discovery. And it auto-updates.
Pro Has a command line interface and a daemon
Transmission can be used in text-only mode via transmission-cli
that includes a daemon (transmission-daemon
), a CLI and a web client (accessed on http://localhost:9091 by default).
Pro Works great on a seedbox with its web interface
Transmission has a web interfaces that can be used to remotely control torrents. It's great as a seedbox (a dedicated private server for uploading and downloading content) due to built-in webseed support.
Pro Pre-installed on multiple Linux distributions, including Ubuntu
For those who prefer Linux, the Ubuntu OS comes with Transmission already installed, so you can get your torrents up and running immediately.
Pro Headless software
Just put it on your server, SBC or even your old phone and you have your own torrent server.
Cons
Con No preload magnet metadata
Transmission is unable to preload magnet metadata.
Con If data is corrupted, torrent file has to be re-added
If you delete a file that belongs to (finished or not) torrent, torrent will remain in "corrupted data" state and only way to restore it (aside from restoring the actual data file) is to find the original file and re-add it.
Con No broadcatching support
Broadcatching is a method of automatically downloading content as soon as it's available. Broadcatching in BitTorrent clients is usually implemented via RSS. Transmission requires manually selecting each download.
Con No super-seeding support
Super-seeding is an algorithm used to allow downloaders become uploaders quicker. Transmission lacks support for this functionality.

Con The app is hiding too much information
While the app is clearly going for minimalism, some users might feel that the default window that consists of just torrents and their progress bars might provide a bit too little information or functionality. For example, even accessing file lists requires opening up a separate window and navigating to a specific tab.
Con No tracker exchange
Tracker exchange functionality allows peers to exchange information about trackers of a given file. It is another way of ensuring that the file is downloaded from the optimal source. Transmission lacks this functionality.
Con No embedded tracker
An embedded tracker allows turning the client into a server offering an easy way of sharing files with others. Transmission lacks embedded tracker support so another method of sharing or different client has to be used to share files.
Con Written in Python, uses a lot of CPU on fast downloads
Apparently, the speed bottleneck is Python.
Con No built-in search engine
Built-in search engines allow finding torrents to download right from withing the torrent client. Transmission lacks such functionality.
Con No proxy server support
Con Sneaky about trial limitation and prices
Trial version only cleans 500 MB, but it does not disclose that limit before one pushes the button to clean after a scan. While it's OK to provide only limited functionality in a trial version, the appsshould be upfront about what the limitation is.
Especially with an app that is supposed to clean your system, it's really messed up to run an activity only partially, and then ask for money. This is clearly done to play on the insecurities of the less-than-tech-savvy users, who might believe that their machine is now in a worse state than before they ran the app, and need to pay now to get a clean system.
Even when trying to close the nag screen by pressing the little X in the corner, the X turns into "Don't leave yet, get your personal discount", which opens the website and gives you even more discount than their "Deal of the day" which is shown after you download the trial. So people who just go to the website to buy pay $89 (or $69 when they get a deal of the day), but when they pay from the nag screen, they only pay $56. That is not a good way to do business, and even if it were a solid app, it's hard to support these practices.
Con Space Lens reports more storage that the SSD actually provides
For example, a 480GB SSD with 70BG free, and the sum of the folders Space Lens shows in root is about 550GB. That's definitely wrong.
Con Provides no info about things it deletes
The app does not provide any additional information about the files it wants to delete, so the average user cannot make an informed choice what to remove and what to keep. For example, it might prompt you to remove languages other users of your Mac are using. That's not a good idea.
Con Uses just a tiny window for showing details about what the app tries to delete
In full screen view, the part of the screen where the app shows a list of things it wants to remove is about 8% of the screen. So you can see 8 items at a time (out of a list that has about 80 entries), and the name of each of those items is truncated. 75% of a 24"-screen is entirely blank in that view.
Con "Flush DNS Cache" will not boost speed
It will simply flush the DNS cache, so that each request for a web page will require a call to a DNS server first.
Con Claims it will "Free Up RAM"
People who have a clue about memory management will understand that on a Unix system RAM is typically fully used, because that is the way to optimize speed. Any attempt to "Free Up RAM" will lead to other stuff being loaded into RAM immediately: the app might "free" 2 GB of RAM, but if you come back to Safari and look at several tabs, it will soon be back to only 200 MB of free RAM.
Con Expensive
A full license is $89, but there's no way of telling how long you would get free updates. Owners of the previous version will have to pay 50% of that to upgrade. The subscription service is $39 per year. If there's a new major version in the next 3 years, subscription will be cheaper. All that fits with MacPaws being intransparent and sneaky.
