I have the GV unit and love it. Makes a bit of a clunk when downshifting but the mfg said that's normal and it does not hurt the unit.
I have about 4200 miles on mine and have hammered on it up and down. It's solid and I'm pushing some decent hp through it. Big block car and it needs the break on the highway.
The only issue I ever had was a dying battery causing a low voltage issue that made the control unit cpu freak out and lock in at start up and stay engaged. Not good to be engaged in reverse I assure you. I called the GV mfg and they were very helpful to assure me no damage occurred when I backed up and warned me about the low voltage issues with the controller. I followed their advise and put a decent battery in my car and have had no problems since.
500 ci bb 3:55 gears and a 727 with 3000 stall.