Yeah, I have been using it. There is no transition or anything like that required, just type
yarn inside a project that has a package.json. Yarn has basically all the same commands as npm, plus a few new ones that are awesome (like
yarn why). In my opinion when compared to just using the npm tool: the commands are tidier and have more features than npm, the docs are more readable, installs are faster, and the init tool is better.
I haven't had any issues with it at all, but I don't use bower for anything.