I play on a Powell with a different headjoint brand then that came with it. When I am out of practice and being lazy, I play on a Muramatsu. I plug all the holes. The holes cause more trouble than they are worth. I used to only cover the D key, but after getting older and having hand problems it is MUCH easier to close them all.

I've got 2 out of my 5 holes plugged at the moment. After spraining my right wrist this year (which has yet to heal fully) my ring finger no longer has side to side movement, and I can't get it to cover the hole without pain in my wrist.