This Golfmechanix scale is well worth the money. I used it on a mini tour player's irons recently. After telling him what the unit does, he wanted to see if it could make a difference. I asked him if he had a favorite iron to which he said, "no, I like them all but wish my 9-iron was bit more consistent." Turns out his 9-iron was the lightest iron in the bag and way out of range from the rest of the irons. Same head model, same shaft as the rest—just an odd ball in the set. After fine-tuning his entire set and bringing his 9-iron up to the rest, he is a believer of Club MOI.
This unit is easy to use, but it can be a bit finicky because it's very sensitive. If you have trouble getting a reading, follow the instructions carefully. If it still gives you an error reading, make sure the unit is on a stable surface and is level, all fans and windy doors and windows are closed, and don't allow the club to wiggle on the beam. Also, make sure you calibrate the unit to your normal working environment, i.e., temperature and humidity. I use it in an air conditioned shop and needed to do multiple calibrations while cooling the temperature down to my normal working temperature of around 72°. The manufacturer says it's factory calibrated to around 77°
I purchased a large, foam filled, blow molded case to protect the unit when traveling. The beam seems very fragile, so I think this is a must do if you are storing it or will travel with it.