ok the putting arc is a good putting aid but it does have its nagativs. The main nagative being that you run the club against the plastic, the putter is actually touching the plastic. whislt you make a good stroke with it as soon as you take it away you stroke will start to dart inside instead of taking it back in a nice smooth arc. the best putting aids are ones that you move the putter inside some sort of train track style aid.
the very best aid i have ever used is a small hole that fits insde the existing hole, brilliant