Did a quick pass of the docs, and the grid system seems to be opinionated/unconfigurable w/r/t changing column ratios as device width scales. Everything is 100% width at mobile size, and once you pass that breakpoint, there's no adjustment mechanism at any other size.
That's a big step backwards from bootstrap's col-breakpoint-width, IMO.
It also fails to address nesting columns within each other.
This feels more like a rudimentary grid system that happens to have some button styles, rather than a "framework".
If you want a bootstrap-like grid experience with flexbox and sans the bloat, I've had a decent experience with this: http://flexboxgrid.com/
Foundation Sites (F6) also comes with flexbox grid btw. It's optional, you can switch it on in the sass settings and use the same html markup as before.
That's a big step backwards from bootstrap's col-breakpoint-width, IMO.
It also fails to address nesting columns within each other.
This feels more like a rudimentary grid system that happens to have some button styles, rather than a "framework".
If you want a bootstrap-like grid experience with flexbox and sans the bloat, I've had a decent experience with this: http://flexboxgrid.com/