I've done them, and they can cause hamstrings to cramp
so, yes, effective.
He is making a couple of errors though:
He's taking the legs too far back and therefore removing the tension from the hamstrings.
He's also lifting his hips off the bench, he should be in full contact with it.
As the weight gets higher, it does get more difficult, and bands would probably be a better option (or bands with a weight that can be got into position easily when alone etc), at least band tension would remain constant, no matter how far back the ROM was, depending on where the bands are anchored in relation to the arc of the movement, I guess.