I wouldn't call it completely painless when I tried it a few years ago. Compile times can be very long for some packages (try installing pandoc and all its required dependencies) and there were definitely a few package that just didn't work, though I don't remember which ones now.

No, it’s not completely painless. You need to recompile a lot of packages and are spammed with warnings.

I have had zero warning spam and no issues and I use it a lot.

If you run `brew doctor` on a brew installation with a custom prefix, you get several spurious warnings depending on what all you have installed.

It's not spam, but it is annoying if you're trying to use `brew doctor` in an automated process.