You can definitely put it into production. It's just not a "pixel-perfect, cross-browser, fully tested on all devices back to iPhone 4" kind of stylesheet. It's a "looks decent with no effort" kind of stylesheet.

It's more to help you launch quickly so you can test an idea, like a hackathon, side project or MVP.

For many it’s usually “back to IE11 on the locked windows 7 workstations of all financial, insurance etc. institutions I want for a client.”