i see that the poseidons are very "sensitive" as well.
What do you mean they are "sensitive"? They do have little quirks like don't turn them on slowly or they will free flow until you get the tank valve fully open. Generally, I find them fairly solid; they either work or they don't. I've never had them seem to work when I tried them in the pool and fail when I got below 100 feet. I have had other regs which seem to be tuned well but turn out to not work as well at depth.
By the way, do you know anyone who has some time on the Hollis 500se? It does look like serious competition to the Poseidon XStream. I also notice that people who sell both are selling the XStream for the same price as the 500se.