Some people love CGBP, for that area of tris i like dip machine, wide-elbow pushdowns, etc. Extensions are not primarily gonna hit the same areas.
Before you give up on any exercise because it doesn't work or hurts, try slight variations in grip, grip width, ROM, angle and keep the reps moderate to high while going as heavy as possible. Worth trying decline CG with an E-Z curl bar or Smith Machine if it's practical before giving up on them. Also vary the grip width, and also try either keeping the elbows in, elbows out or not doing full ROM-lower the bar only part of the way down, stop well before hitting chest. Smith Machine can sometimes be better on some exercises, like CG. Trial and error, see if there's some version that works and doesn't hurt. Go as heavy as possible while keeping the reps moderate or high, rests of a minute or less.
Same thing with any exercise that either hurts or isn't felt in the muscle, try slight variations in grip, angle, etc. it's surprising the difference small changes can make in effect and in injury avoidance. That thing about going too heavy when younger's very typical, Mel Anthony was talking about that too in a recent mag article, we all regret some of those things we didn't know then. We can learn how to be more efficient and easier on the body later with more experience.
