You also can't feel a 3hp increase even if you see it on the dyno.
I use my gtech pro RR when i'm tuning. I'm after ACTUAL on-road increases in acceleration, not what result i can get at one dyno, that will then be different to another dyno's result.
If you have free access to a dyno, well you are very lucky, but for someone like myself i cannot justify several hundred dollars at a time in dyno sessions. It's easier for me to find a flat stretch of road out in the middle of a deserted industrial estate and perform my datalogging there.