I know it's been discussed, probably buried in the archive now.
I had a passing curiosity a couple of years back. Further search, not in the MB world but in cycling circles, lead me to opinions they were pretty much junk as far as components and build quality.
Then I actually looked at one off craigslist one day near me and they were right. It was junk and the whole auto shift thing was really hokey. IIRC it was an AutoBike, one with the centrifugal weights on the spokes. Thing is the best MBs end up being the simplest, cruisers and hardtail mtbs.
I think there is at least one other make out there, landrider or something. I don't think any of them are going to turn the world upside down but what the hey, if they are cheap enough and you think they'll hold up.