x2 on all of the above, I think they started out being somewhat reputable for 4L60's in the LS world, then went to garbage coasting on a good name. I looked into a 6L90 a while back, cost for the unit was the same as a local shop quoted (but without install). Their ready to go unit that would get me running (Main reason I was considering them) was rated at 380 HP when those came factory behind a lot of 6.2's rated at 402 HP, and that was before I did the cam swap to put it closer to 475 HP. Their built unit was still barely rated for it, and I took the info to a local shop who had that combo pegged as a "level 1/stock performance rebuild". Local guy got me a parts list that was solid for 500 hp and turnkey price was about what Monster wanted for their "Monster" unit.
That said, I think most of the negative reviews are more along the lines of overselling their capacity like that, along with a fair share of "Blew up as soon as it was installed", but probably if it is running ok and you aren't pushing the limits of what it is "rated" at, you're fine for a while.