Personal preference I guess but I think the mini starters are better than the stock starters in every way possible. They spin the engine faster, sound better, disengage and stop almost immediately (no waiting for the thing to wind down and stop spinning if the engine didn't catch the first time), are lighter, smaller, more clearance to the exhaust, and as I will explain below are cheap and long lasting if you buy the right ones. I have (no lie) at least 10 mini starters currently in use on both small and big block engines. The big block ones I just pop off that extension thingy and they fit fine, no grinding.

As far as where to get them- I bought one from MP years ago and it crapped out, I've bought a couple from parts stores over the years and one of them crapped out (replaced under warranty and still working today), but most of them I get from a pick n pull yard for around $20, find them on 90's era v8 truck and van (used factory units). These are the freakin shizzle as far as I'm concerned, they seem to work forever and they will whip a hot or high compression engine over no problem. Nuts to the expensive store bought pieces.

For the O.P., try disassembling it and check that the internal connection from the main electrical power lug is connecting to the solenoid. It should split internally to send power to the main body windings and the solenoid. Try jumping it there to see if it pops the pinion plunger out. It's either the connections or the solenoid itself, it's not real complicated to figure out once you see how it is constructed.