Hey, congrats on getting the C. I just keep on getting more impressed with mine.
Regarding mags, OEM are 17 rounders, MBX are 19s. I ended up getting the only extended basepads I could find in stock during Black Friday for the OEMs -
Continuous Precision's +2s. That gave me 10 mags all carrying 19rds. They do not have the same floorplate dimensions, btw, and to the best of my knowledge there aren't any extended basepads for the MBX.
When I first received the MBXs, frankly, the follower looked like gen 1 3D printing. Just terrible layering, look and feel rough as hell. These followers are a little wonky, so I have concerns about tilt and reliability. Presently, in my mind, they are range mags only. But, I am open minded to them proving themselves over time. I have thus far had zero problems with them, but I probably have less than 20 cycles on each yet.
The factory OEMs are $70 each, and the extended base pads are $35, getting you 19rds. The MBXs are $109 for the 19 rounders. So it's a wash price wise.
I'm right at the cusp of unhappy with the MBXs, because of the crap follower manufacturing, but they've given me no performance problems so far. But I also wouldn't recommend them yet. I'll be getting another 5 of the OEMs at some point soon, but will continue keeping the MBXs in rotation.
EDIT: All the the mags load tight - the tightest I can recall having ever used, for any gun. Last round requires a lot of force with your thumb, and when you're shooting in volume that gets old. Do yourself a favor and
pick up one of these. They work far better than I expected, and far faster than loading mags manually. After using one for the Staccato, I picked one up for the DWX Compact, and it made everything extremely efficient. Probably cut mag loading time by about 2/3.