I've had one for about two months now and I must say I really like it. The power output is really nice from my 440.4. (75wrms @4ohm, 220wrms bridged) I was going for a budget SQ setup, and it worked well. It has more than enough power to drive my single 10" beyond what is enjoyable. (IMO, I don't like overpowering bass, and and don't need to turn up components so loud to compensate it makes my ears bleed :'( ) Easily makes all the mirrors shake.
The crossovers seem to work pretty well. I only have two complaints:
There is no anti-thump tech installed. If you just turn off the car, your speakers will thump. Not real bad, but annoying. Cured by turning off HU (and amp) before turning off car.
Second, The amp requires 4ga connections. Seems a bit much for me. They even "require" ~12 ga wire for remote turn on wire, yeah right.

I've
heard of people running 8ga to it and its fine. I ran 4ga, not a trouble since I have a single amp install. You
will need spade terminals for the 4ga going in. The amp terminals are not big enough to accept bare wire. You can jam maybe half the 4 ga wire in, but this a sloppy way to do it, and will probaly only result in the wires pulling out, and the connection looking like a half-assed s*** job.
Overall, I would say this a a great inexpensive high-powered, clean sounding amp. Not a lot of frills, but not really needed. Build quality seems really great, but only time shall tell. Gets warm during operation, but I've never come close to a shutdown (under seat mounting. 2x4ohm front, 4ohm bridged rear) For ~220 shipped, and 3 yr warr (as I recall) this is a great deal.
Also fits nicely under the drivers seat! The 600.4 would have been cool, but I don't really
need that extra power, so I saved the 80 extra bucks. If you don't care, go ahead and get it.

The 400.2 would be killer, as would the monoblocks. G/L either way!