Really good, but has one flaw: It does not take the available product variations into account. It should disable the "impossible" buttons, just like the default (dropdown) does.
Example: I have shirts in red s, red m, red l, blue m, blue l, blue xl, blue xxl.
When i select "xxl", the "red" button should be disabled (and so on). Or it should at least mark the "red" button as unavailable/incompatible with the other option(s).
And for the feature wishlist: Being able to have radiobuttons for some attributes and dropdowns for some.