the two FBO advance plates i have are very inaccurate.
It is very much trial by error. I also make sure to deburr them before using them as I have seen them hang up occasionally.
But having said all that, they are easy to use and change, I don't weld so welding the slots instead would be a challenge. I also think they work better on real Mopar distributors versus the current repros, the Mopar distributor weights are beefer and the axial play is less with the spring clip set up.