yeah, my A.D.D. messes up the cluster all the time, I don't even run it any more unless I'm going to the track. The smarty shouldn't have that problem though. Anti Defueling Devices tap generally splice into VSS and Tach Signal wire and then change the signal on the output side, to the ECM. The fact that you are cutting and splicing wires is very bad in and of its self.
With my BD
unit, they supplied connectors that were much to large for the gauge wire being used, and would disconnect, causing my gauges to go out, the truck to stumble at idle, and even die at any given throttle position. Everytime you use the device, it will throw up trouble codes and I've lost other gauges because of it as well.
Smarty on the other hand, is a programmer, it puts a different program in your stock ECM telling the computer to let the truck fuel longer, change fuel curves, reset and correct speedo and ABS, and displays and I believe clears trouble codes as well.
I wouldn't recommend an A.D.D. If you are racing a lot and don't want to shell out the cash for a smarty or red line and want to fuel into really high Rpm on the line, then they'll do the job, but if you're daily driving it, they are not worth the hassle, I didn't have to pay for mine and I still don't think it was worth it.