I have never purchased any, but I have been given heaps---I personally would rather spend my money on the game and instruction. I was given one of those putting green strips--that sucked...oh and one christmas someone gave me this little plastic gismo that had a ball on the end of plastic swinging arm... It would tell you what type of shot you hit, etc...the second shot I took sent the plastic ball and swinging arm straight across the room and imbedded itself into the wall next to the xmas tree---NICE!!!!
I tried a friends double hinged Medicus once---6 swings to perfection or was that the inside PVC foam jobby from Jack---anyway the Medicus was alright for setting up tempo and pretty decent at swing plane. I liked that you could hit balls with it as well.
Gee I wonder what I am going to get this xmas.... I hope it is lessons...