I have attended his one-day "Bulletproof Mind" class. I thought it was very good.
Most of the in-service police training classes I have attended appear in the encyclopedia under the heading "five minutes of worthwhile information stretched out into eight hours of stupefying tedium." It was a pleasure to actually attend a class where it was easy to pay attention and where I didn't find myself looking at my watch every thirty seconds.
I think that even those people who don't agree with LTC Grossman's opinions will probably agree that he is a compelling speaker who does an excellent job of keeping the audience interested throughout his seminars.
Cogito ergo summopere periculosus.
Fiat justitia, ruat coelum.