Based on what I've seen in the forums, nobody thinks using Mani is a good idea. I'll stick with SourceMod, but I'll have to figure out what is and is not okay to do.
I believe SourceMod is causing clients to crash. We've played several games with SourceMod on our server, and some players would periodically crash. Without SourceMod, everyone can play happily.
It would be really nice to have SourceMod play well with GE:S, it's an indispensable admin tool in my opinion. I guess I'll try to figure out where the problems really lie. I'm leaning towards map voting right now, as crashes tend to start happening when a map votes starts or concludes.