1. What's different about this version?
This unofficial version of ACE3 is the last one before the medical rewrite. A lot of people found the rewrite to be rather glitchy or incompatible with their mods, so this version is here to help you out.
2. How can I check out what's different?
Check out the files and acquire the source code via a tool like PBO Manager. https://www.armaholic.com/page.php?id=16369

Steps are like this:
A. Go into your Arma 3 Launcher and make Cobalt ACE a local mod.
B. Check out the Addons folder, and see the relevant PBOs.
C. To open them up, use PBO Manager and a config unbinarizer like Unrap.

3. Does this work with UMO?
No. This version of ACE3 like the official one places a limit on movement speed coefficients, and so it will not work with UMO.

4. Does this work with Advanced Armor Plate Mod?
Yes!

5. What about missing dependencies for ACE patches?
You'll want to use only one version of ACE3 at a time. Do not run two at once or things will get funky. Ignore the dependencies.

6. Why use this instead of normal ACE?
See #1