I like their site, but ironically the big “download” button they’re using doesn’t appear to have been made by Button Builder. At least, I didn’t see it in the library.

I think that’s true for almost any button there. The default included themes are from the 10.2 days. There is a helper application to help you build themes, but you have to have the design created yourself.

After spending some time on the RealMac Forge site, appears that one of the major tasks for the next release will be more themes. A well deserved update, I’d imagine.