I've shot the standard BFG with the old brake and the new shark brake, I have also shot the BFG Carbine. The new brake cut the recoil by about 30% and made a big difference. The BFG Carbine that's here in SoCal is Mark's personal one, he's pretty much donated it. One of the guys I shoot with is a dealer and does all the local gun shows, besides selling Anza knives, he sells BFG's and Windrunners. I think that's why Mark has left it here with him, he also brings it to the range for anyone to try out.
If I were to buy one it would be the Carbine, you can actually shoot it offhand and with all the upgrades it's actually comfortable to shoot. If you go over to Biggerhammer you'll see how big of a following that Mark has, plus he posts on the board. He's a great guy and completely stands behind his work.