I could care less about free maintenance and the warranty. If I had an M3 and was curious about the superchrager, I'd be more worried about how an engine running at 11.5:1 compression ratio (and an 8K rpm redline) would handle it.
I don't know though....if I owned an M3, I'd be looking into the potential of air intake, exhaust, chip, etc. rather than a supercharger since those mods provide better reliability. But that's just the route I'd take...I'm sure there are M3 owners lining up for that E46 M3 supercharger.