When comparing Default Folder X vs ImageOptim, the Slant community recommends ImageOptim for most people. In the question“What are the best power user tools for macOS?” ImageOptim is ranked 8th while Default Folder X is ranked 39th. The most important reason people chose ImageOptim is:
Great for compressing images for web usage or saving harddrive space.
Specs
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Pros
Pro Directory assistant Finder Integration
From the Open / Save file dialog, you can access your recent, favorite, and open folders. Includes a menubar item and can add to the Finder toolbar for quick access.
Pro New features are intuitive
Many of the features provided by Default Folder are quite intuitive and quickly become very useful. When a save dialogue is open, just click on an open Finder window to change the current path to that directory. Integrated Quicklook previews make selecting files in the list view much easier, and Spotlight tags can be added directly from the save dialogue.
Pro Losslessly compresses PNG, GIF, and JPEG images
Great for compressing images for web usage or saving harddrive space.
Pro Fast & Simple
Pro Simple drag'n' drop interface
Simply drag images (or folders) into the window.
Pro Tries several different image optimizers before picking the best one
Pro Edits files in place
It does edit files in place, overwriting the original. This is exactly what I want, so I love it, but it's good to know beforehand.
Pro Can handle PNG, GIF, and JPEG images
Great for compressing images for web usage or saving harddrive space.
Cons
Con Compression algorithm not as good as counterparts
Con Cannot abort an optimization
Optimization can run for a long time. Sometimes it reaches 20% quickly and then spend a long time to attain 21.2%. But you cannot interrupt the process.