not slower - no way.
wiring - yes. PITA. but it's not that bad once you know what to do. You only really need to connect 6 or 7 wires to your original car harness.
availability - they are mostly in demand by the dune buggy people. If you sniff around a bit you can find all kinds. As for parts - well it's basically the same engine as the US ones (for the most part) and any part number I have taken to the dealer has resulted in me receiving the part in a couple of weeks. Even if it is a JDM part.
Like i said - I am not being an armchair theorist. I have one. I installed it. I've messed with my 2.5 NA. The turbo is not fragile - I have never DNFd in my rally car because of it. It hauls at 16 psi on a whimpy vf11. It cost so little that if I blow it I'll just by another one for 500USD and swap it out. there's no point even opening it up!!