I had an M-1000 for awhile like 12-14 years ago. I thought it was fine I wouldn't hunt one down, but if I could get one for the price I got mine for or an 800 for the prices people are asking for those, I'd stick with the Metaltronix.
It sounded like what it was supposed to sound like, in the Paul Gilbert/Zakk Wylde sort of land, assuming you had the appropriate guitar going in. I recall it being a bit "sticky", as opposed to fluid gain. And a bit woofy, but I mean, that's sort of to be expected.