My first gym had one; they actually had the best selection of leg equipment of anyplace I've been.
Yes, there's more focus on the quads and a lot less pressure on the lumbar region, which makes it remind me of front squats with a barbell - in fact, if your gym doesn't have this style of squat machine, the front squat is a good alternative.
All of the guys who had lower back issues tended to use this machine, the Hatfield bar for squatting, and the reverse-hyper bench for decompression.
