The biggest difference IMO is the inability to back the drag all the way off on the TR3. So when you're setting gear every pull to get your line out requires a good yank. May not be a big difference to some guys but drove me bonkers, especially when using MR3s at the same time. The set it and forget it drag thing isn't perfect either, still requires a bit of tweaking to really lock it in after you've put tension on your rod and a little backing off once you have a fish on. Maybe it's just me but I find having the ability to loosen and tighten in a bigger range advantageous.
As far as a 0-10 drag setting range goes it's like this:
MR2 0-8 with free spool option
MR3 3-8 with 2 turns of the drag knob
TR3 6-10 with 1 turn of the drag knob
I prefer having MR2s as an alternative to the MR3s (I have two of each) both for the smaller and lighter size on lighter rods as well as full free spool for dropping for lings.