If your club's sorted, then this shouldn't be a problem, I've flown at 2 differing FTO's, the first used to pair me with an instructor for a while and then change if he was unavailable. This meant I ended up flying with a number of differing instructors, not a problem if you get on with them, however I had a definite problem with one guy and told the club I wouldn't fly with him again. On the flip side, I flew with an Airbus Captain who s**t hot on PFL's!
Club I fly with now only has a couple of instructors, I always get the same one (providing they don't cancel the lesson!), which is cool, 'cause she's a babe!
I do think the pupil (as the customer) should have a say, after all it's no good being stuck with an instructor you detest!