I had the unfortunate (read stupid) experience the other day of neglection to put the brake on my 270 Am.
The first shot caught me by so much surprise when 12 lb rifle reared back and jumped nearly off of the pedestal rest, and the scope put about an 3/4" carf on the bridge of my nose. I didn't notice it until I look in the mirror later that day. Didn't break the skin......
Chrono reading were spot on normal. POI was spot on and group size, I shot two more, was typical for the rifle.
Thus, I gather that with that specific rifle it makes no difference, brake or no brake.
If you want to test another rifle, come on out and we'll take the brake off of the 338 RUM w/300 SMKs and you can give it a go. Not me