I don't have the 70-210, so can't comment on the IQ one can expect from it but, can say that it's kind of big and heavy. I do have the stablemate of the 28mm 2.5, the 24mm 2.5. I don't find the 24mm 2.5 to be a great lens. It's not very sharp wide open and even when stopped down to 3.5, my Pentax K24 2.8 is sharper and has better contrast wide open. I hope this info is helpful to you.
Regards, hex anon.