I cannot recommend the Taly enough. I am usually not a fan of trainings aids because so few of them work. But the Taly works incredibly well. Unfortunately I got away from using it for the past 4 months or so and I'm going to get back to using it now.
The big thing about the Taly for me is that it provides visual help so the golfer can get into the right alignments instead of being a training aid that forceably puts the golfer in the right alignments through some type of restriction.