I've shot a 26" barreled 16lb 300Win mag with the Ops brake it worked realy well recoild was less than any of my 12-15lb 308's and I coulden't tell any differance in the muzzel blast from that gun to an unbraked one. I have never used a KDF but one similar and dien't care for it , it did reduce recoil but it was loud.
I like the Vais and Holland styles alot they work realy well I have a Bennie Cooley Tactical style brake here that will probably be put on a 7mmDakota long range rig that will be built for my uncle it looks like a realy good desgine. I have used the regular JP brakes and they are totaly awsome for recoil reduction.
check out www.jprifles.com
and take a look at them both