You also might want to check out Bourbon Neat for your grid system, which has been doing this for awhile. Rather than extends, it does a lot of this through mixins. Their breakpoint system is also pretty nifty.
In general although I appreciate the larger CSS frameworks from a documentation and organization standpoint I find that their expanded use over the last year to lead to the "Oh, this was built with X" sameyness in a lot of new projects across the web. You even see newer frameworks like purecss.io that are trying to remove the actual styling from the framework itself, concentrating instead on base elements. I'm curious to see how this will all transition over the next couple years.
I'm a frontend designer myself so I'm biased, but I think relying heavily on any of them too much can limit your product once you get past the prototype stage. That said, I've learned so much over the past year just being able to look through their documentation and see proper smacss principles at work on large projects.
In general although I appreciate the larger CSS frameworks from a documentation and organization standpoint I find that their expanded use over the last year to lead to the "Oh, this was built with X" sameyness in a lot of new projects across the web. You even see newer frameworks like purecss.io that are trying to remove the actual styling from the framework itself, concentrating instead on base elements. I'm curious to see how this will all transition over the next couple years.
I'm a frontend designer myself so I'm biased, but I think relying heavily on any of them too much can limit your product once you get past the prototype stage. That said, I've learned so much over the past year just being able to look through their documentation and see proper smacss principles at work on large projects.