It'd be better to have a three-point expert PG who can replace/backup Rondo when there is a need to spread the opposing defense. But 3-point skills, good ballhandling, good playmaking, good passing, and good defense all in one free agent player is probably too much to expect from what the team is willing to spend. Arroyo would not be a bad choice. He seems to fulfill most of the above and perhaps that is reasonable for what the team is willing to spend, unless they want to touch part of the MLE. He might be on the selfish side, but then again, it's not like the Celtics have offensive weapons on the second unit/bench anyway. So maybe you would want Arroyo attempting most of the shots from a reasonable distance when the second unit is out there.
Whatever happened to Jason Williams? Would Williams be better for us than Arroyo? A flashy player could be entertaining.