If he gets of on command and is not known to be aggressive, shouldering is fine. It's when they won't get down and/or may attack your face it's a problem.
Kiwi bit me in the face, twice, and while he wasn't on my shoulder at the time of the bites, he wasn't allowed on my shoulder because he had shown himself to be dangerous at that point in time. I used to bend my arm and hold in so he couldn't/would struggle to climb up there and give him a firm "no". Yes, he did in fact bite my arm a few times for that too. There is arguably dominance issues that can arise from being on eye level with you and in a position to inflict damage (parrots are smart and manipulative). A worse case scenario with a large parrot is damaging your eye, nose, lips or ears irrevocably. Arms and hands can take far more abuse. Has only been in the past year or two Kiwi has been allowed on my shoulder, as we seem to have overcome the aggression issues and he hasn't bitten in a very long time.
But from what I've heard about Bonkers, he is a very mellow and friendly bird and it likely won't cause any problems at all. It's birds who behave like Kiwi did when we adopted him who should not be allowed on shoulders. For trusted birds, it seems to be an organic scenario between human and parrots and can actually be a bonding thing

Unless Bokers does something that would make you be concerned about him being up there, I really don't see any reason he shouldn't be.