I had a .270 Win with a BOSS. It was the Browning "Eurobolt" model (Schnaubel forend, low lustre stocke, matte finish, funny bolt handle) that I saw in a gun shop and fell in love with it....it was certainly something different, I liked that about it. The owner made me a sweet deal and I jumped on it.
Got her well glassed and dialed in. Gun shot wonderfully at the range (with hearing protection).
Hunting was another story. First deer I killed with was extremely unpleasant....my ears hurt & rang for days.
I shot my buddy's 460 S&W revolver (ported & braked)with earplugs and muffs on. It simply was no joy.
I never again want another muzzle brake on a gun.....period.......ever.............
I have a Browning A-bolt in 280 Remington with the boss system. Most accurate rifle I've ever shot. It had the ported system to start with. I sighted it in and them changed to the non ported system. It's been shooting great ever since.
I've had a .300 Win Mag with a BOSS for 12 years. I like to load and tinker and shoot a lot. With neck turned, plus other tricks, WW cases, my rifle shoots 165 gr. Hornadys in to 3 shot groups that measure with calipers .187". If you let the barrel cool a bit it will stack 5 into the same group. If I had a scope stronger than 10X I think the rifle would shoot even tighter. I've had and have, a lot of non bossed rifles in a variety of calibers and this rifle simply outshoots them all.
Loud yes. Especially in thick woods. But I use ear protection on the range and mostly only 1 shot in the woods. No problem.
My son and I shot my 7 Mag., his .243, and my .300 off a bench one day. We both agreed the .300 felt better against the shoulder. IMHO recoil reduction is a huge plus in accuracry.
Put it this way; If I wanted a .243 I would want one with a BOSS. That's how impressed I am with it.
I have two Brownings with the boss. A 22-250 and 223. Both guns have little recoil and are very accurate. I'm looking to buy a used one in .338 .325 or 7MM for my elk hunting this fall.