Magnets. The limitless 3.0 has magnets that allow for magnetic mounts and wallets to work. Qi charging still works when these things are not attached to the back. Aside from these two things they’re almost identical I believe.
The contour has a more rounded back and the leather one I got has bigger grain than the leather on my limitless for my 10SMax. I’m really liking the contour but they are both very similar.