I put my ECM back to stock with the tuner and then tried to use it on a buddy's truck. The tuner is VIN locked and will not work on another ECM except for the diagnostic side.
My tuner went back to Superchips four times for reprograming. The first time because it would not recognize my ECM after the initial install (I wanted to change the performance level). They fixed that but then the speedo calibration disabled my ABS and the ABS light flashed all the time. After three more returns to Superchips they fixed that. The tuner works well now and the speedo is corrected for my 33" tall tires.
As I stated before, there is a significant power increase with the tuner on my truck but results vary on others. On some there is no noticeable power increase.
I would NOT buy a used tuner, unless they have made some programing changes it won't work.