I have had both stage 1 and stage 2 H-Dev chips in my old S13 and also H-Dev stage 1a in my S14 many years ago. No problems at all.
Drove down to see Jez and get him to install the chip in my 14 about 15/16yrs ago, really nice guy. Very helpful on the phone when discussing options - he didnt push his own stuff on me, we talked about a few different options and I settled on his own stuff in the end.