But here's the short version: if you just care about performance of audio plus a few extras (balanced, stopped volume pot, software mode, etc.), Mezzo is it. If you like the AK100's functionality as is, but want better sound quality, RWAK100 is the way to go.
If you find AK100 to have too much noise from HPO, there's only one choice: Mezzo. I have a very hard time picking a winner as the two are mutually exclusive mods.