Have you shot it yet?
My 21a is very picky about ammo. I shoot CCI Mini Mags or faster rounds in it (Yellow jackets, for example) and it shoots beautifully. But, it tends to choke on standard velocity rounds.
If yours is the same, isn't that going to be a problem with suppression? Or do you get enough extra pressure with the can that it will cycle normally with sub-sonic rounds?
I works just fine dry, and is how I have shot it mostly. Still nice and quiet. I'll try some wire pulling gel or plain old water eventually to see if it gets much quieter. My experience in the past with rimfire cans is that wet doesnt make enough of a difference to deal with the added mess