When comparing FTP Synchronizer vs Polo, the Slant community recommends Polo for most people. In the question“What are the best GUI file managers for UNIX-like systems?” Polo is ranked 13th while FTP Synchronizer is ranked 19th. The most important reason people chose Polo is:
Polo wants people to get the file manager they want, but it's not awash with granular layout options that take ages to understand. First select whether you want one, two, or four panes, and then select a format for each pane of either List, Icon, Tiled, or Media. That's it, you're done.
Specs
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Pros
Pro Can sync multiple files across multiple websites in parallel
With FTP Synchronizer you can synchronize multiple files and multiple sites simultaneously.
Pro Can schedule syncs
You can schedule when you want to synchronize a particular document for a particular website.
Pro Very secure
Supports syncing over FTPS and SFTP.
Pro Does not waste time by copying every file over
When syncing a folder, FTP Synchronizer intelligently finds out which files have been changed and copies only them.
Pro Purposeful layout choices
Polo wants people to get the file manager they want, but it's not awash with granular layout options that take ages to understand. First select whether you want one, two, or four panes, and then select a format for each pane of either List, Icon, Tiled, or Media. That's it, you're done.
Pro Installs smoothly on Debian, Redhat and Arch based distributions
File managers in Linux have a nasty propensity for being closely tied to the distribution family from which they arose. Using Polo allows you to have an identical file management experience when shifting between machines from different branches of the Linux tree.
Pro Device management
Quickly mount and unmount devices from the sidebar, including support for locking and unlocking LUKS encrypted devices.
Pro Youtube-dl integration
Just paste a YouTube URL into a folder and Polo will download the best quality format of it and save it in that folder.
Pro Archive browsing and creation
Browse archive files as those they were just another folder, dragging and dropping files in and out of them at will while the backend uses the appropriate tools to manage the archive file itself. Archive creation includes a rich assortment of controls over compression formats and structure.
Pro Image file actions
Rotate, resize, optimize, convert formats, save for the web and many other handy features all right in the context menu.
Pro ISO file tools
Mount ISO files to loop devices with just two clicks, or spin them up as a QEMU KVM instance, and for portability there's also an option to write them to USB flash drives using a GUI dialog.
Pro Advanced PDF file controls
Perform Merge and Split operations on PDF files without needing another file handler all from the context menu. Rotate and Password Protection settings are also expressed there.
Pro Cloud storage support
Includes its own rclone macros for adding cloud storage access to the list of browsable locations that just works, a welcome relief in the sea of hacks which provide those features elsewhere in Linux. Currently supported: Dropbox, Google Drive, Microsoft OneDrive, Amazon Cloud Drive / Amazon S3, Openstack Swift (Rackspace Cloud Files, Memset Memstore, OVH), Hubic, Backblaze B2, Yandex Disk
Pro Views
Supports up to four panes, plus a tree-style side panel and tabs.
Pro Terminal emulation
Built-in terminal pop-up.
Pro Launchpad PPA available
Debian-based distributions can leverage the apt package management system to keep Polo updated by adding the approved PPA to their apt sources, simplifying installation as well.
Pro Permissions management
Features a file properties side panel to easily assess and modify permissions.
Cons
Con Overpriced
Even using single license mode no longer functions correctly. No longer sending emails as it says it does.
Con Freemium model
Many of the best features mentioned as pros are only available after a one-time donation of USD$10 or more. Until then you just have a fast, good-looking and otherwise forgettable file manager.
Con No drag and drop
You can't drag from one view to another.
Con Load loop
Slow opening with annoying 'load loop' dialog.
Con Lengthy beta cycle
Polo has been in the beta stage of development for longer than hoped for, and while mostly stable, isn't yet ready to be promoted as a rock-solid replacement for file managers such as Dolphin and Nautilus.