I have 4 of the 2010's and a stack of the 2510's. I use them each and every day with excellent results. Got them from Staples during various promotions. Paid an average of $30 a piece. Figured cheaper to buy the entire printer than just an $85 replacement toner cart.
Main differences are:
2010 rated print speed 22ppm
2510 rated print speed 25ppm
2010 cart can be refilled easily.
2510 cart has a "fuse" that has to be replaced at the same time as refilling. At least that is what I am told. I haven't used any of the 2510's yet as I have been refilling the original 2010's carts.
All in all, they appear to be almost the same printer. The 2510 does lack a top panel mounted Toner Saver switch though.