There is a lot of Voo Doo out there about brakes. I spoke to numerous manufacturers at the last shot show and most agree that the hole size is not that critical for recoil reduction. But of course you have to have safe clearance. I have at least eight muzzle brakes on everything from a .224 to a 45/70 Contender. None of them have been machined to match. I screw them on and check clearance with a cleaning rod.
In fact, I had a .224 brake on my 220 swift that was bored .015 over and I did not like that (did not feel safe) but it shot great and I never had a problem. But I wanted to put a JP 3 port comp on my 220 swif so I moved that .224 brake to a .204 and it works awesome; in all fairness I did not have another 204 Brake to compare it to, BUT....
The JP brakes have a .281 exit hole, suitable for anything from 204 up to 6mm. I put one on my swift and one on my 243 Long range and they are awesome. Somehow it shrank my group from my 25 year old swift from 1/2" with factory ammo to 3/8" and that gun has over 2500 HOT loads through it. And 4 prairie dog shoots. The 6mm brake hole is way bigger than most "experts" recommend and my 243 shoots like a 22 LR. For ***** and giggles I put my 30 caliber JP eliminator on my 243 (it has a .350 exit hole) and it too works great, but I need it on my 300 win mag. I put the "appropriate" JP 3 port comp on my .243 and I can't really tell the difference. SO, in my opinion, with testing... try different things just make sure your barrels and brake holes are reasonably aligned and have sufficient clearance. Don't go crazy trying to eke out every last .001. ALSO, regarding timing a brake, unless you have a special purpose, 12:00 straight up is timed. If you start tryoing to mess with counter rotation techniques and side thrust, you will drive yorself nuts! And, you can do a "reasonable' 12 o'clock up. I try to get it so it doesn't drive me crazy by eye. If you don't shoot with a bubble level your brake will not be firing up at 12 or out to 3 and 9 o'clock anyway.
Just my 4 cents, based on my a lot of experience and trial and error.
The guys who are saying they get 40% reduction in recoil and they machine the **** out of everything to be perfect.... what if I screwed on a "sloppy" brake that gave me 35% reduction? Is all I'm sayin'.
On another note, radial brakes LOOK cool. I shoot over dirt, a lot, Target shooting in the desert, prairie dog shooting in the ... well, prairies and there is a lot of dirt and dry stuff and radial brakes are out. Besides, you want downward and rearward thrust, not upward thrust! You just have to look at the original tank brakes on anti-tank guns from the 30's and 40's. They knew what worked back then and nothing has changed, except the way people want their equipment to look.
ALL of that being said, if you have the money or capacity to have the brake fitted to the barrel it is definitely nice and preferred. Is it necessary? Not unless something is grossly misaligned, which I have not experienced yet.