I would pass on the Pac-Nor brake. Simply put...they really aren't nearly as effective as many other brakes on the market, and, thanks to the porting 360* on the brake, it'll kick up dust/dirt/@#$% like nobody's business which can be a royal pain in the eyes when shooting prone. Also, unlike the Vais which actually has the forward-pointing ports aimed toward your target, the Pac-Nor does not which also makes it LOUD compared to many other brake designs.
The Fat Bastard brake is one of the best around for maximizing recoil reduction, but they too are LOUD!! As for the install...Pac-Nor should be able to do it. It'll need opened up (I think that they ship with a 7mm opening which you'll want opened up ~0.328" or so for your 300WM), as well as timed/fitted to your barrel, but it isn't rocket science and should be well within Pac-Nor's abilities.