Hey - Austin from Mantis here. Happy to answer questions.
Yes, it uses accelerometers and gyroscopes.
The current version of the app won't work well in your typical competition scenarios. As dr poopgiggle pointed out: there's too much other noise that can mess up the data (is that a hard stop or a bad trigger pull?). We're working hard to add that capability going forward. The current version is really geared towards static shooting, focusing on core shooting mechanics, common shooter issues, etc.
For holster draws, we designed some mag floor plate replacements that basically add a rail to the floor plate. But that only gets you to your first mag change, so...yeah, it's best for non-competition stuff at this point.
And yes, it's much easier to reverse engineer on Android.
The firmware on your unit is probably just streaming live data to the phone, so nothing too interesting there, as all the analysis happens app-side.