I just got one. It's going back. Dark, dark, dark with my VTL-225's. It muddies up the sound, sucks out all harmonics, 12-hour break-in didn't help. Better pc didn't matter.
The P300 Power Plant is a definite improvement, the Ultimate Outlet isn't, especially for the price, and the fact that you need to use a premium cord instead of the wimpy AC pc that comes with it. Can't recommend it. Monster HTS2000 power conditioner strip is much better, only $130. Your system may yield a different result, but I'd tell tubed amp owners to forget it. I'm pretty disappointed, after waiting a month or so for it.
BTW, the Outlet's choke radiates a significant amount of EMI, which can't be good for your system. I heard a spitty edge on highs that sounds like an EMI artifact. Locate it far, far, away from components and ic's, unshielded pc's.
DO NOT sit it on top of PS-300.