The effects you feel will depend on the type of brake you choose and the caliber and velocity. With a 308W you are right. Probably not going to feel much. Which takes me back to my post, about 4 posts back. I said it all depends on what you are after. I was going to ask why you even felt the need for a brake on a 308W but it wasn't my business. If you want a brake by all means do it. I have 3 rifles with brakes and I use them for the purpose of being able to see the bullet strike and to make recovery from recoil a little quicker. They are all Vais brakes so most of the side effects are felt more by bystanders than by me. At the risk of repeating myself, you first have to ask why you want a brake. From there the decision gets easier.
The baffel style brakes work better. I have two Jp breaks and they work great they reduce recoil more than any other breaks I have had. Vias style breaks are okay but they don't reduce recoil like the JP or other good tank style breaks. Reed
The JP is absoluty the most effective of the bunch you mentioned , if you can stand the looks then it will give you what you want.
Typical I have seen that the muzzel blast to the shooter is alot less than to anyone standing of to the side.
I just had parrysgunsmithing.com put on one of his custom on a 300rum and as with the KDF and Vais that I have all work fine and do what is expected reduce recoil. I can only comment on what I use and of the four different makers I couldn't say one is better than the other. Well good luck.