Why would you choose an unknown though when there are tons of battle tested frameworks out there? The only reason I can think you would do this is if the framework offered something totally unique or revolutionary, but I really haven't seen that in many frameworks for a long time now.
Then why aren't you using Cobol (I assume you're not) :-)
Seriously it is probably a good idea to look a little at new things and possibly try one out and later switch every few years. I could be after 5 years or after 10 years but you can probably find things that helps a lot with some projects. Regarding the unknown one might want to differentieate between things you don't know and things almost no one knows about (ie very new things), the latter aren't really battle tested yet but the former might be.