It’s a neat little offering from Japanese company Elecom. They’re just optical mice (wired, at that) with the somewhat interesting function of having internet browsers’ “Back” and “Forward” functions specifically attributed to those two side mounted thumb buttons.
Of course, I imagine you could configure your current mouse to do just that with the software that came with it (if you paid more than, say, $15 for it), but this one is made just for that, and the buttons are thumb activated.
I love italicses.
Anyhow, they seem to go for about $40, and will start selling in mid-July. In Japan.