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,I'd still go for the Apeks.
Sell the other stuff and get a new Apeks rather than the Poseidon.
What I am seeing here is a LOT of brand loyalty. Without looking at these regs, it's impossible to give you a qualified opinion as to which one is best to service. There might be verdigris where there should never be in anyone of the regs that would make me hesitant to service it. Look closely at your regs and even into the sintered filters to see if there is evidence of flooding or neglect. If you aren't really sure what to look for, and your loaner won't mind you selling their regs, then get rid of all of them and start afresh.