I use the Sport and with that model, if you keep the wheels in contact with your scalp (and no or little pressure on the blades), it works great. Lift the wheels and you risk a nick.
I found that with the ATX, that wasn't the case. I found that the amount of pressure on the blades had to be significant and it had to be changed with each change in contour. I could not get as good as a shave with it.
I've also seen others comment that they had to lift the wheels off the scalp to get the right angle. Someone even stated that they keep the wheels off for almost the whole shave.