When comparing Material Files vs OI File Manager, the Slant community recommends OI File Manager for most people. In the question“What are the best Open Source and ad-free file managers (with root explorer) for Android?” OI File Manager is ranked 2nd while Material Files is ranked 3rd. The most important reason people chose OI File Manager is:
It asks only for Storage permissions. No other things are required.
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Pros
Pro Open Source
On GitHub with GNU General Public License v3.0
Pro Few permissions
It asks only for Storage permissions. No other things are required.
Pro Lightweight
The app takes only a few seconds to download, as its size is only about 1.5 MB to download and installed (on MIUI) takes only ~6 MB full size.
Pro Open Source
OI File Manager is available for free under the Apache License 2.0.
Pro ZIP file extraction support
OI File Manager supports extracting ZIP files.
Cons
Con Enhancements desired
As this is still relatively new, there are a number of enhancements to make this feature parable with other file managers
Con No additional features (suite)
No other features such as networking connections, junk flies cleaner, built-in media player/viewer/editor. But that might be a pro, since nothing else is asked for this app permission.
Con Outdated
At this moment I'm writing, it was updated last in 2017.
Con Ugly UI
The GUI is old and deprecated. But what would you expect for such a small app?