When comparing Dolphin vs fman, the Slant community recommends Dolphin for most people. In the question“What are the best file managers for UNIX-like systems?” Dolphin is ranked 3rd while fman is ranked 13th. The most important reason people chose Dolphin is:
As with any KDE app, Dolphin, allows adding or modifying toolbar buttons and keyboard shortcuts.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Immenseley configurable
As with any KDE app, Dolphin, allows adding or modifying toolbar buttons and keyboard shortcuts.
Pro Can split views
Dolphin supports splitting the view in two navigational areas, this way you can navigate two different directories at the same time.
Pro Integrated terminal
Pressing F4 with any opened folder on a mounted path opens a console within dolphin.
Pro Also has a refresh option
Dolphin is without a doubt the best fully functional and easy to use and multitask with.
Dolphin also has a refresh button which no other File manager has. It's great for tracking a large files transfer; that's what file managers are for - good common sense.
Pro Easy to extend with plugins
Dolphin follows KDE's philosophy of being extendable and configurable. It can easily be configured and customized through plugins.
Pro Auto mounts flash drives
Dolphin automatically identifies and mounts external flash drives.
Pro Fast at opening graphics folders
Pictures with or without previews is optional and selectable at the touch of a button.
Pro Does not use third party libraries
Unlike all those GTK-based file managers it does not have to rely on external written software for its functionality because KF5 is KDE SOftware and developed alongside.
Pro Keeps its state
It starts with last opened folders.

Pro Fully supports HiDPI
Supports HiDPI displays.
Pro Automatically centers items
In icons view mode, the space between files gets stretched so that there is never and annoying empty space at the right side of the window.
Pro Works on all operating systems
Windows, Mac, and Linux are supported.
Pro Simple to use
Pro Makes finding commands *by name* easy
Pro Slick
Cons
Con May be a little slow on startup
Dolphin can be a little slow on startup (depending on distro, hardware etc...). Startup time can vary from a couple of seconds to up to a minute.
Con Can hang on remote file systems
It doesn't cope well with remote file system nicely like sshfs or any samba, like when network is not responding/very slow. It just hangs.
Con "Type" column too verbose
Despite having a large enough monitor, if you keep the size of the browser window small, the "Type" column (in "Details" view mode) insists on including the complete multipart MIME string, making the column so wide that trying to limit its width makes the column useless. Sorting by "Type" renders the list into an incomprehensible mess.
Con Poor optimization on later versions
Con Too simple
Feels weird on KDE because it has less customizing options Konqueror and any other KDE app have.
Con Can't perform ROOT actions
Developers set a constraint in Dolphin that deny Dolphin to run with root permissions. Hence, if you want to perform an action that require root permissions, such as rename a file in /etc/ folder, you are forced to use terminal or switch to another file manager.
Con No (text) file viewer
Con No explicit bookmark support for directories
It though remembers the visited directories and allows to search in this list in most-recently used order and by name.
Con Mainly for key-board-orientated users
The interface is most naturally navigated by arrows and keystrokes. The target market is software developers.
Con Has no menu bar
Hence it is not well suited for visually orientated users which find or remember commands by using a mouse and a menu. Even the fman's hero Sublime Text uses a menu bar.
Con Requires email address to download
Doesn't say what it will do with this data. It is in contrast to the new laws in Europe where only necessary information is allowed to be collected. A download should not require an email address.
Con Still quite buggy
So, for example, sorting only is remembered if triggered by command and not be clicking the table column header using the mouse.
Con Settings can't be found by the GUI
You need to know which files to edit.
Con Default dark theme
No choice between dull-dark or fresh-light.
Con No portable bundle available
On Windows only a net-installer is available.
