To the OP, the purpose of my first post was really asking if you've considered other options. It appears your based in the uk, so am I. I've yet to see an explorer on a dive boat here, I've seen few of them at lakes/quarry's. If your intention is to dive this unit in the uk you won't , IMHO, find much support from other divers in terms of experience, spares or buddies on the same kit.

I'm not here to promote or defend the inspo (or YBOD if you prefer) the manufacturers can do that for themselves. But if your going to rebreather dive in the uk the most common units used are the inspo and JJ. My suggestion for a used inspo is based on my guess at your budget and the advantages outlined before , which I imagine also apply to the JJ.

I can't be arsed to argue over electronics, age of design etc, however , the quote re service or lockout is complete rubbish. There's a recommended service interval but no forced requirement to send the head back. Whilst all parts function correctly the unit will continue to dive or tell you something's broke and give you options of how to dive.

From my own research when looking into units I believe the poseidon unit does have a required service interval and will , after warnings, lock you out.

Which ever unit you go for, think hard about where your rebreather diving may take you and plan, purchase and train to the best effect.