The problem with pointing devices is they're too small, not too big.
Context of how it's used is important though. Shape is as important as the size of the mouse. Regardless, this doesn't appear to be a replacement for your standard sized mouse. It seems to be a replacement for your already undersized travel mouse, which is too small to be used like a normal mouse and too large to be used in any other way.
If you watch the video on the homepage, you might notice that it looks the most awkward to use when people are trying to use it like a normal mouse. There's a part where the guy is making sweeping motions with his arm and wrist like he's playing a game. That part looks silly.
Then watch the people who are using mostly fingertip control to nudge the Swiftpoint around on the surface of their palmrest. It looks a lot more natural then. It's like what ch_123 said about how clueless people use trackpoints like a joystick. The name of the product is pretty accurate. It's not so much a mouse as it is a "point" of some sort.
If people learn to adapt to a claw hand-like style, this product might be onto something. If everyone just gets frustrated that the wide sweeping wrist motions that they're used to are so awkward, they're doomed to be a novelty product. I'm afraid inertia will win. Everyone will just blame the device rather than recognize that it's really not a mouse.
As someone who already does a lot of claw hand on the mouse, I'd be especially interested in trying one of these. I don't use my laptop that often though and I'd be loathe to give up my big trackpad and I'm not totally sure that this is any faster than a good trackpad. On my ASUS netbook or my old Dell Laptop, it's a great replacement. On my MacBook Pro, it's probably a step sideways at best.