I have both the Driver and Iron versions of the Momentus Swing Trainer and I still love them after two years. I have the driver model in the car for when I won't be able to hit a driving range before a round, but have a few minutes in the parking lot. The iron I keep in the house and swing for at least ten minutes a day.

The idea takes the 'heavy club' idea and forces your hands, arms, stance, etc., to support a much heavier club when going through a normal swing. This forces you to slow down, be more mindful of positioning, etc. It also works to increase strength and flexibility.

At $60 its a good deal, I purchased mine when they were $90, and I've now seen them at Target for $30!

Only downside is that you can't actually hit a ball with the original (it is too short and not designed for striking a ball.) Newest models now allow you to hit the ball at the range.