Re: muzzle brake symmetry and accuracy?
I agree with the principle of the claim that even/concentric gas dispersion is important for best accuracy. Hence for "ultra" precision, I would think that no brake would be best for your bench/rail gun.
For good precision on a hunting rifle, there are a number of good brakes and I have only praise for Holland's QD brake with baffles to the sides and holes on top. I've had good experience with other designs as well such as KDF. But, Vais, Muscle Brake, Painkiller, etc... all have great reputations.
You'd be hard pressed to convince me that one of these is inherently more accurate than the others. As discussed by previous responders, poor quality materials and/or installation will render any design worthless.