An M5 would be an ideal solution because I could also use it for effects that I wouldn't use much, like Uni-Vibe or flanger (as well as the aforementioned reverb). I'm not really thrilled at how my EX-7's flanger sounds in the effects loop. I thought it might be because most Soldano amps have an effects loop that assumes rack gear, but the JCA22H doesn't. Any pedal should work.
It's hard to know how much to trust sites/reviews that talk about build quality. It shouldn't be a big issue for me because it will probably never leave my office. Of course, Brad Paisley tours with an M13 (and a ton of other pedals) so . . .
What do you primarily use the M9 for? Time-based stuff?