You won't find any old threads about the SFB, all the threads are right here, because it's not out yet, and it's not old enough to have old threads about it yet.
I'm going to sound like a smart a** saying this, and I really don't intend that way, but the FB can do things a folder can't. It's the same size and dimensions, but since it's fixed, theres no need to worry about lock strength, blade play, keeping lint out of it, etc. It's also 440C blade steel, since it's a fixed blade, it has different carry options than the folder.
Think of it as yet another upgrade.
At the size of the SF and SFB, lock strength really isn't an issue, because you're probably not going to be prying with the Biscuit, but for SD issues(which this knife is perfectly capable of handling) deployment becomes an issue. A fixed blade can be deployed faster than a folder most of the time.
Some people prefer folders, other prefer fixed blades, this gives both camps a chance to partake of the holy SUBCOM design
Really, it's just another fun option to have. I would prefer the fixed blade, if only because it'll make a heck of a neck knife, which is something I enjoy.