Common as in that specific system, not really I don't think. Useful, I suppose. I've seen and done similar things, but not with a clicker. You can just say yes/no, etc. It's helpful for them to get immediate feedback while they continue and figure out how to make the changes without being positioned, although I think it works better with older girls. The problem is if they don't fully understand, they'll just keep on going...you have to be sure that both partners really understand what you want, otherwise it can just confuse them more. We used to do routines and the coach would tally it and once every lock that was "hit" earned a piece of candy. That was because she had a bag of candy left over from Halloween, usually it just got tallied and a yes or no. Poor lock positions are one of my pet peeves too.
I think "random" reinforcement is just as useful though once they get the idea but just have to work hard to always do it. We used to have to do so many of something right and if the coach saw one wrong, start over, or make 5 in a row, show the 6th, if you don't make it, start again. Or do a routine, if you miss so many lock positions, do 10 rows of step lock, etc. That can be demoralizing if you're not careful but sometimes they just really have to always do it and not just do it when it's the "focus" that time. So I think it's helpful for them to get the idea of doing it consistently, but once they can do it, I prefer to have them go about a sequence and reinforce the problem areas from a more random standpoint than just repeating the same skill. They seem to get more out of that - but that's just my experience. Initially in trying to correct a problem or weakness, I do find repetition very helpful though. Sometimes they're just not aware of how the "right" feels vs the "wrong."