This is one of those things where you can ask a hundred people and get a hundred different answers. Personally it depends which system your talking about, some of the cheaper systems may be out a little bit, I use a Hudy setup station w/ tweak plate on my TC and it's very accurate and consistant. My advice would be to talk to the racers at your local track and see what differents systems there using and what they think of them.
tweak and setup stations are only as accurate as the surface you are using them on. if it's on a un-flat or wobbly surface, they are worthless. if they are on a flat, solid surface, like a granite countertop or something, they are fine.