Jeremy,
You will hear tales of both good and bad with bellcranks. I'm currently building a TF Corsair and didn't use bellcranks for the ailerons but wound up using them for the flaps. It's all about the quality of the hardware and installation. NO slop is key. I used Dubro bellcranks and a nylon threaded locknut to anchor the post screw then placed the bellcrank on top of the nut. That will eliminate loosening of the post and slop. Clevises not Z bends for the pushrods. If your not lined up (pushrod to servo arm) ball links solve that problem. Bellcranks work but you need to work at it
Pete