Andy,
I think you need to be a bit careful about what you read here.
I had a late version of the original MT and now, with my Baja 5Bss and my XL Octane have an XB (got the 'XB before the Octane).
I had problems with getting the original MT started, which In the end I fixed by replacing the carburettor, I also had a throttle servo fail after a few hours of running, but other than that it was pretty solid. My XB has been no trouble at all although I don't run any of my models much. I have an engineering background, and from this perspective, having examined both close up (in fact when I finished with it, I dismantled the MT competely). They appear to be well engineered and robustly made. But I guess it depends how you use them, and what you want from them. I personally don't thrash my models to within an inch of their lives so probably don't get the problems that others may have.
Hope this helps
Harvey