I have had mixed results.
I put a mini starter on my V8 Fiero project. It worked great at first, but died quick. Come to find out, rain, water, etc, would run off the deck next to the rear window and drip on it.
So, I pulled it out, cleaned the corrosion, sealed it with RTV on all mating surfaces, reinstalled, and never another lick of trouble.
My buddy that bought my old 85 383 Vette put a G.M. authorized mini starter (see it in the GM performance book). He had to get it rebuilt twice in less than 5,000 miles.
The really awesome ones are on the late L98, and LT1 engines. The 1989-96 Vette has this super cool high quality gear reduction ministarter made in Japan. It kicks! They sound super tight and smooth starting as well......you have all heard a late C4 start...right?
If I had my choice on a small block, I would go get one of those...making sure the flywheel was the right diameter to match.
I have a mini on my big block right now. It is okay...nothing really to brag about, and it cost about $140. Small, light weight, quick starts. It is a win, win.