It's developement version, but I wouldn't call it super-buggy. WebKit project has strict development process, each commit is rigourously reviewed and tested before merging.
You will likely run into problems if you enable experimental flags though.
You will likely run into problems if you enable experimental flags though.
These sorts of temporary issues aren't that a big deal if it's in a separate application that you use only for testing, but they're a darn sight more painful when you replace your system WebKit frameworks and they start impacting things like your email client or the system installer stack.