I suppose it depends on what you mean by custom.
Ive been fit by bettinardi and bobby grace and edel. They all thought my alignment was good.
I have had a lajosi where lots of features could be specifically customized.
Ive also had putters refinished.
Reclaiming putters and making them pretty was more fun. To be clear i sent the heads to a craftsman for rejuvenation. Im not handy that way.
I think as long as alignment is good, then long as the hosel matches the swing and the swing weight (read feel) is right, most of the putts you were going to make you make, and most of the ones you were going to miss you still miss. It’s hard imo to identify the incremental value. Jmo. Ymmv.