When comparing photoqt vs FastStone Image Viewer, the Slant community recommends FastStone Image Viewer for most people. In the question“What are the best image viewers for Windows?” FastStone Image Viewer is ranked 1st while photoqt is ranked 10th.
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Pros
Pro Highly customizable
Pro Support many image formats
Pro Simple
Pro Really fast
Pro Lots of features for simple editing
Pro Great for comparing and sorting multiple images
Pro Free
Pro Best keyboard controls
Pro Editing photo levels
Pro Built-in folder browser
Can browse folders, images and videos, all with thumbnails.
Pro Has dark mode
As well as Gray mode. Good for your eyes.
Cons
Con Windowed mode is a little bit awkward
By default it hides your window manager frame so there is only basic window management features provided(what it says in the setting).
But you have an option to show the system's window manager frame if you want.
Con Free version is not valid for business usage
Only good for private use, small business licensing is very expensive.
Con Broken SVG Support
SVG images do not show at all.
Con Sometimes really sluggish
Showing the wait cursor for multiple seconds like executing large operations in the GUI thread.