Bogie - can you expand on your comment that the Dremel batteries "didn't fair all that well?" As I understand it, these batteries are identical to Bosch 12v battery, with the exception of the base plate. I've read that 30-40 minutes of run-time is expected.
Did you have significantly worse runtimes than that? I'm also curious what, specifically, you like better about the M12 2460 vs the Dremel 8220?
We were typically pretty hard on our tools but my experience was the new batteries were just fine. Within a couple months we got 20-25 minutes on a full charge. Within a year they got replaced. Definitly harder on them than an average at home garage user, though my personal tools dont get beat on too hard.
Weight and ergonomics between the two and run time are what leaned me to the M12, it just felt better using in my hand. Secondary is trying to get into one type of battery platform that meets all my needs. The Dremel is just under 1.5lbs IIRC and the M12 is just over 1lb, depending on which battery you use, and they have a few battery sizes to choose from. Sure, an XC 6.0 would add some serious weight, but give great run time if needed. Small job or limited access...grab a 2.0.
When/if I get around to buying one my Dremel will still be hanging, ready to use, until it goes to the land of the misfit tools.
V/R
Bogie