I have a green Victor I got for my step-daughter who no longer plays. I upgraded it a bit and it's now a loaner. It now has E-grip, green Gen-X reg, Rocket valve, green CMI barrel, and a few other things. It's very consistant and reliable.
My son's 2nd gun is a BTB Rebel electro (yeah I know not a Kingman) , and he also no longer plays. I decided to see how low I could get the pressure on it. Yeah I know low pressure isn't all that, but I wanted to see what I could get. With a Check-it Powerstation reg, Magnaport valve, some spring work and a 14" System-X barrel. It'll now do a very consistant 285fps +/-5 at ~250-ish psi on anti-syphoned co2 without a valve spring (yes it actually works!). Also it's now VERY quiet... went from the usual stbb 'KACK' to more of a 'thup'. So there IS something to this LP thing, at least on cheap blowbacks.