Hi, metal bassist here.
Just thought I'd write a positive note about my PF500. I've had this thing for 2 months now and I've had nothing but a good experience. I'm pairing it with an Ampeg BSE410h and I'm getting an amazing tone from it. It's no SVT, but then again it doesn't cost $1400 or weigh 90 pounds. Even with just a 410 8ohm cab this thing is plenty loud for the venues that we play in the area. I've only played two gigs, a handful of band practices and nightly practices at low volumes but it seems like a solid, well-built amp so far. I haven't had any problems with it cutting out although I thought it crapped out on me at our last gig. We we're opening for a tour coming through Portland (Overkill, God Forbid) and the amp decided to lose power half way through our second song. Turns out it was just the venue's outlet that was crapping out, go figure

. I play thrash metal and here's the tone settings I use to get some beef and gritty punch out of it:
Gain: 1-4 o'clock depending on the bass
compression: off
ultra lo: on
ultra hi: off
low: 12 o'clock
mid: 3 o'clock
mid selector: 2-4 depending on bass/mood I'm in that day
high: 12 o'clock
volume: 11-2 o'clock depending on situation
I'm loving this amp so far. I'll give an update in a few weeks after I've played a few more gigs with it.