I’m going to simply say that the Dave Pelz Shoulder Alignment Mirror is the best one…..for my students.
I also like the flat left-hand rest chipper to get people a good solid structure and sense of impact for little swings and chip shots I forgot who designed that clicker as well but I use it and I think it’s called clicker Tom Nas showed it to me at the golf digest schools the first year Tiger Woods won his first Masters in 1997