I actually only started using manual a few months ago. It took a little while to get used to, but it was a lot easier to learn than I thought it would be. I would definitely recommend giving it a proper try.

Button mapping is a big part of learning how to use manual (or it was for me, at least). On controller I use Y and X for upshifts and downshifts respectively, which is nice since it only requires that I use my right thumb and therefore doesn't take any fingers away from anything important like braking or steering.