I have them, and really enjoy them. I also like Gunnar as an instructor. They are excellent core/functional fitness workouts. They are meant for all levels, but are more intermediate (any easily modified to beginner). I make them a bit more intense by adding reps (while Gunner is setting up the next move). Otherwise, you only do 6-8 reps for most moves (though some are 16-20, like some ab work). I love to use them during recovery weeks, when I don't do heavy weight/intense workouts.
The best ones, IMO, are the Accelerated core training and "Full body challenge" from the first set, and "Off the ball" and "Accelerated Training Camp" from the second set (which doesn't use the stability ball for all the moves, like the first series does.
I did a combo of "Accelerated Training Camp" and "Off the ball" yesterday, and my glutes are really feeling it! You don't use heavy weights, but the moves really use a lot of muscles for stability. My butt DOMS is probably from the 1-legged deadlifts and reach lunges (a lunge done while reaching toward the front toe with a weight in one hand).