I have the Grizzly one. I have read all over mini-lathe.com and several others (varmint al, vickie ford, gadgetbuilder, etc). I'm also a member of just about all of the mini lathe yahoo groups (except the 7x10minilathe one, which is 99% politics and religion anymore, 7x12minilathe is always on topic).
These lathes are pretty much all made by the same company, SIEG, and are pretty well interchangeable. The various companies change more than just paint color, though. Micro-Mark adds a digital read out and some metal gears, maybe even a cam-lock tailstock, but in the end they're the same machines inside. Lots of parts from one fit the others.
Most consider this class of machine to be JUST enough to get you started. That is, out of the box, they may not be quite ready to go machining press fits and such. They have a lot of sliding/moving parts that need to be adjusted finely to operate well. The downside is that most of the sellers don't do this for you. The upside is that you REALLY get to know your lathe during this process.
Once setup, cleaned and tuned nice and tight, you can machine to quite fine tolerance ... a thou or less, I'd say, if you're careful with things.
They're not rigid enough to take a 1/8" deep cut in stainless, of course, but you can really move along with aluminum. My first threads turned were in CR steel and they sucked big time - turns out it was the steel, not the lathe. My next set of threads in aluminum did fantastically. I've since turned a half dozen or so more threads and all of 'em are very clean and functioning very well. The nice thing about turning your own threads is you can make 'em as tight as you want so there's very little play when tightening 'em.
The grizzly's a nice lathe because it comes lots of accessories. The best price out there, thoguh, is toolsnow.com - they have the most accessories.
Also - beware of the designation 7x10 ... it's actually 4" shorter than the 7x12 lathes. Someone had a math goof somewhere back in the day.
It's perfect for little stuff. It does a great job on aluminum (6061), brass and delrin. I'm told it does really well on 12L14 steel, too - i'm still keepin' an eye out for that.
If yer interested, it's a great way to get started.