AJ- I sincerely doubt the Gardner photo is a composite. I've seen enough CDVs to have a pretty good sense of these things, and that group looks too consistent in lighting and posing to have been pasted together from individual images. Also bear in mind the size of the image - the original is only about 2 inches by 3 inches.
John - I agree, the Gardner group portrait is absolutely masterful in the overall group composition, which makes me think the head clamp is intentional. I also noticed that only one of the sitters, the right-hand-most woman, is facing the camera directly. I would love to find out who this group was. Even if I could only identify one of them for certain, it would probably point in the direction of who the rest of them are.
Holm- I think the most curious thing about the daguerreotype is the absolute plain-ness of the set. It's just the two people. I've seen lots of dags with plain backgrounds, and lots with some kind of set as well. Maybe this one seems all the more striking because there's just so much plain background visible. Regardless, the image is a striking one to me (which is why I bought it).