Kirby is installing a Slim PainKiller version on my new 300 WSM. He stated that it will reduce recoil more than the Vias, and it won't throw nearly as much dirt up when shooting prone. I've got the same brake on a his Raptor 338 AX, but haven't shot it yet. All the 300 mags I've ever shot had brakes on them. One had a Vias, and it was good, the gun was plenty shootable.
Last fall I shot a 338 edge quite a bit, it had one of Shawn Carlock's brakes on it. I believe it is similar to Kirby's PK brakes, but don't quote me on that.
I have shot unbraked sporter weight 7mm rem mags, and didn't find them enjoyable to shoot at all. Heck, even my dad's old 270 with a steel butt plate just plain hurts after 3 shots!
Downside to muzzle brakes is the added concussion and noise. We can get around the noise with good hearing protection, but I still feel and notice the increase in the concussion (kinda like a really strong gust of warm wind hitting you in the face all the sudden). Still, I'd rather have a brake then not on anything 7mm mag or bigger, especially if it's a light rifle.
I've got a Vias style on a heavy very heavy 22-250. That rifle barely even moves when shot. But it's only shot off the bench.