CSS was such a mess for so long because of the complete lack of a consistent easy-to-understand layout mechanism. This has spawned the creation of countless workarounds and javascript gizmos, JUST SO you could stick something on a webpage where you want to go and have it behave in a sane way under resize and different browsers.
I welcome CSS grid, it reminds me of the sane layout managers we're used to from writing desktop applications. It makes me wonder why we had to wait so long for this functionality to be part of the CSS standard.
As for the generator, I think it's nice. Most folks will get the hang of banging out arbitrary css grid layouts very quickly. This tool will accelerate that for many.