I am just trying it out for my side project (https://www.gettandem.com) and liking it so far, however the time will tell... (it's WIP so nothing is polished).

I was considering either no framework (as before), Tachyons and Bulma. After quick demo of moving one page to Bulma I liked it enough to give it a go.

To the argument of CSS grid vs flexbox, as others already mentioned, it's kind of implementation detail from the user point of view.