I'm currently using this in one of the send returns of my Roland Gp-100 as another preamp. The Roland is an excellent hidden jem. It's preamp is damn good too, but it's a bit tough to get a classic marshall sound out of. I then run them through a sonic maximizer and into a VHT 2 90 2, the BEST POWER AMP IN THE WORLD !!! Anyway, I have to totally disagree with some of the other reviews in the section. This preamp is cable of getting just about every Marshall sound that ever was. You can get anything from literally the cleanest clean to extremely heavy. I'm quite a tone nut and this thing is pretty darn good, and a great value for what you can pick them up for used. I play all styles of music from jazz acoustic through metal. This is a Marshall, don't expect any other sound, although the cleans are something in themself. Don't get me wrong there are better preamps out there, but there aren't a lot to start with. Sure you can get a 3 or 4 channel preamp from quite a few companies, but if you are any kind of gigging musician who doesn't have time to fool around with knobs, and you actually care what your sound is like then they aren't flexible enough. You need something midi. This has a much more analog tube sound that anything Digitech has ever produced, but look for things like VHT (even though its 3 channels its quite flexible) Soldano X99(expensive but very good) Engl 580 (THE BEST!, I'll have one soon) and the Roland GP-100 very good preamp with very good effects. There are only two real complaints I have with the sound of the JMP. 1. It gets quite noisey at med - high gain levels, even with a real quiet power amp, and 2. if you are using any sort of high gain pickup it will feedback super quick if you aren't careful with volume settings. All in all Marshall in 1 rack space.
It seems reliable enough, I've never had to deal with marshall, but I use it gigging all the time, and have had it opened up a few times, and it doesn't really seem like anything could easliy break in there.
Overall this is a very good preamp, that needs to be used carefully, but is easy to use. Fairly well feature packed, with good tone when dialed in right. It has some noise and feedback issues, but just make your own patches and you won't have to worry about them. It's a steal used going anywhere from 300-450. Use it with good gear and you should have good results...your setup is only as good as it's weakest link.