Had this for a week or two, replacing a RBC2510. First - an extra 6cc of power, seems like a doubling of power! this thing has grunt to spare; I'm running it with my usual setup of alloy head with 3.3 diamond edge and its a bloody handful ( in fact I've just ordered a spool of 2.7 off Dean - never thought I'd go back to woosy sizes). Second - the extra weight is noticeable on big jobs (I'm not a big bloke though), on reason I got it was the 2510 was vibrating too much with 3.3 and is affecting my hands ( the start of HAVS I suppose), the 3100 is very smooth no matter what size/length string - am wearing AV gloves all the time though regardless.
This machine is as said, a bit of a handful with heavy line and I wouldn't recommend it if you're not well experienced - that said, I love it and expect it to be faultless with the 2.7 for standard work. On ferals, I doubt the 50cc machines will get used again, this is a beast with wide open throttle in any situation.
Definitely recommended - Makita quality brand name & Robin/Subaru engine - bewdiful
p.s. one 2510 is now a dedicated hedger/polesaw, the other a backup