So I had a little while to have a play with this tonight. Wow, it is such a sensitive circuit in terms of biasing the transistors hey. Initially my thoughts are it is quite hissy when engaged. The sweep of the trim pot is SUPER sensitive. It seems to react differently to single coils and humbuckers in terms of dialling it in. Humbuckers seem to always have a slight edge of breakup thing going on (not always a bad thing) no matter where the trim pot is. But I'd prefer it to be a clear compressed situation. I'm going to play with it a bit more and possibly try some different op-amps / trannies etc. for a little while until it starts speaking to me. A fun little beast of its own though, which is super fun.