I've seen video clips of Royal Blood before and have always liked the sound he gets out of his bass set up. Unfortunately for me I'm lazy and don't want to go through that amount of trouble.
I think I'm one of the few people around who has a T-Rex Quint Machine. The "pro" reviews seemed to be generally positive, but the few "average Joe" reviews I found seemed to be more negative than positive. But the pedal seemed to fit my needs so I gave it a try. I was primarily looking for a way to produce a power chord (I wanted the 5th above and octave above) and, unless I spent a lot more money, that seemed to be my only choice. Somewhat luckily I found a B-stock model at Musician's Friend so I got a nice discount on it and it arrived looking brand new.
Honestly, my opinion of it is mixed. It can sound synth-y when you raise the level the 5th and even more synth-y when you raise the level of the octave above, plus the lag for the affected pitches is kind of noticeable. If I was using it strictly as a pitch shifter, I wouldn't keep it. But it does seem to do a tolerable job of the "power chord" effect that I wanted - as long as I keep the levels of the 5th and octave a little lower than the dry signal level. Subtlety is definitely the key to using to using it in this application. And, FWIW, I find the lag can actually help fill out the "power chord" effect, but I also notice the effect sounds better when I play simpler, less busy lines. I also find other effects can muddy it up as well, so I don't use it with distortion, etither. Again, subtlety is the key.
If I was in a situation like Royal Blood, then I doubt the Quint would be good enough. However, it's not an effect I use often, only when our two guitarists play a solo in unison or they play harmony solos. In that application, it seems to be a minimal trouble, acceptable solution. At this point, my band is just working on building up enough material to start playing out, so I'm only using it for practice now. We'll see if/how my opinion of the Quint changes if we eventually do start playing out.
FWIW, I haven't had a need to use the octave below and I haven't played with it much. So I can't really offer much of an opinion on that function.