I have ridden with Jeff several times (in CT, actually, before I moved south.) I’ve also audited a few times.
I have seen him focus on one rider once or twice, although I never had it happen to me in a group I was riding in.
I saw it several times when there was a weak(er) rider in a group that was really struggling and it appeared to be the kind of situation where things could go south and wind up with someone getting hurt. In other words, he wasn’t focusing on a favorite, he was trying to ensure that the less capable rider got some benefit out the session even though they were obviously not up to the same tasks given the more advanced participants. And I will admit that in every case, the riders who had to wait around while that weaker rider got Jeff’s individual attention/modification of the exercises, were mostly pretty ticked off. It is hard to pay that much $$$ for a group lesson if you are spending a big percentage of the time watching the clinician babysit a rider who has put themselves in the wrong group, while the horse you are sitting is getting cold.
That said, I personally thought his exercises were terrific and I learned a ton. He is a very articulate trainer and has a fabulous eye for detail. I’d ride with him again in a heartbeat.