GoKawiilLet's start with the basics—the dirt on the field, as it were. The design choices here are all about the aesthetics of the camera, not how it works. I could argue about whether that's good or bad, but either way, it's important to know before you consider buying one.
In my 15 years of reviewing cameras, I've always refused to use the phrase "feels good in the hand," but, well, I'm going to come very close right now because I think it's important to say that the Sigma BF feels very bad in the hand. Bad enough that no one in the design process could have missed it. The body is a single piece of machined aluminum—a beautiful metal box with no concessions whatsoever to pedestrian concerns like ergonomics. It's awkward to hold, no matter how you try to do it. A one-handed grip feels downright dangerous; using two hands works, but the BF still feels clunky and sharp. Because, well, it is.
The simple truth is, this camera is unpleasant to hold for long periods of time. You could get around this with a third-party grip, but then you lose the aesthetic appeal, and at that point, you're going against the spirit of the thing.
The BF features a 24 megapixel full-frame sensor in a very blockish, extremely minimalist body. The body is lightweight and available in either black or silver. It takes L-mount lenses. Sigma provided me with a 35 f/2 DG lens, along with a 90 f/2.8 DG. I primarily shot with the 35, which weighs roughly the same as the body and feels pretty well-balanced. I'd be curious to try the Sigma 45 f/2.8 DG ($619), which is marginally smaller and lighter and might feel better on the BF body. Even better than that would be some pancake lenses, but so far, Sigma has not made any for this body.
After months of shooting with it, I don't mind that it's chunky and awkward to hold. The only thing in the overly designed body that bothers me is that there's only a strap anchor, which means you're limited to using wrist straps exclusively. I find this odd, simply because it seems like at least one market for the BF is the person who likes to have an aesthetically pleasing camera hanging around their neck, which isn't possible here. There may be some straps out there that would let it hang vertically, with both sides of the strap on the single anchor point, but none of the straps I tried worked this way; the anchor point was too small to get both sides of a strap attached.