The advantage is that they're all designed as integrated systems - so the arm and cartridge are optimally matched; no compromise for interchangeablility/compatibility. The downside is the same; one is saddled with proprietary cartridges (
a la Apple Corporation's products - any flavor you want, as long as it's white!).
Fortunately for us, Soundsmith has kept the cartridge format alive (
albeit at a fairly high price, but, heck, we're talking a very low volume, probably handmade article of commerce).
In terms of the turntable itself; b&o's philosophy was rather different than the
status quo - then or now. The platforms are typically light (even flimsy); arguably more style than substance;
but, I would opine, very much fit for purpose and the
systems perform quite well.
I would call the sound of the b&o MMC cartridges as dry but accurate - not bad at all, and the tangentials track quite well (I have a TX-2 and I like it, although I am not using it these days).
Mark me down as a fan, if not a rabid one