And another analogy I'd point out is if you're in Photoshop (or in browser), and you use something like icomoon app to make a nice set of font icons and then style some texture/shapes/etc. behind it for something pretty nice. I feel like that would be a completely valid and workable approach...that said, sometimes you'd want to make the artwork from scratch yourself and that would be valid too
Hrm, no real UI framework. I think a bit of backbone and some jquery libs like scrollto and pretty-something for the code samples (it's all in the view source hehe)...anyway, the real magic of how this works for those inclined is it's a gh-pages branch for the site, which makes jsonp requests to heroku where the buttons are compiled per the options you've selected, and then finally archived and returned to user. It was a fun constraint to work out but turned out to be doable and fun...but guys, pretty please don't DOS it :)
Guys, I sit somewhere in the middle on this. In fact, I'd say the ever hated "it depends"...are you in the prototyping phase? Have you toggled off the Buttons you don't want in the Builder page? If you're really into customizing, have you just considered stealing some of the raw ideas and/or scss? Really, we wouldn't mind :) Here's another approach...say you just want the pills and like the general direction but want to tweak it:
Go to the builder page, remove all but pills
Go in to the _options.scss partial and tweak some more
Optionally take all of what's left and then refactor to your liking
I'd claim you save some time with above and still get a fully customized button.
Regarding using something like Bootstrap "out of the box" is not something I'd personally want to do once getting my project into production...but again, I'm fine using for just prototyping and then tweaking the styles later. That said, to each is own
We updated the library with a Button Builder which allows you to include or remove only the buttons you need for your project (perf matters!), and added a couple more button styles too. Enjoy!