Thanks for the answers. To put the case in concrete terms:
I'm familiar with maintaining Apeks and Mares regulators. Is APD comparable with these or is it advisable to exchange the regulators?
I know I'll go to hell, because I'm not that orthodox, but I'm not interested in GUE
A used APD costs (in my country) about 2k€ less than a used JJ of the same age.
Which one would you recommend?
I have owned a JJ for six years. I live in the U.K. today I am on holiday about 3 miles from APD. I chose the JJ over the APD because of the then monochrome handset and the plastic box. There are a few details of the ADP, such as a big oring that gets removed for a scrubber refill, which are improved on the JJ.
The APD has a bunch of extra technology: temp stick, co2 sensor and BOV which JJ will not sell you. I have a Divesoft BOV which is ironic as I prefer stuff to be stock. One objection I have to the APD is that everyone (ok, half the owners) seems to mod them and the mods look like a JJ.
The JJ philosophy is being simple and robust. APD is prepared to be more complicated.
My JJ has had two failures, one was the ADV shutoff failing, I replaced it with an identical one from APD. I had a head failure too. One of the Shearwater boards died. It was about £250 to fix. I also had a HUD crushed on a boat. Another £250. It fell off a bench on a boat on another occasion, bending the stainless steel handle. 30 Euros.
I would buy another tomorrow. I could live with an Inspiration though, I think I might break it more though.