I've just started playing around with Rendr. If I ignore the learning curve and oboarding friction, I like it a lot and I plan to write my next large production app using Rendr.
Unfortunately, as bababa listed above, the documentation needs a lot of work. There is an explanation of how Rendr works in its README and the example app's README but beyond that you'll need to source dive in order to figure out how the gears are turning. Currently, there is no forum for questions (other than stack overflow :D) and I've had a hard time figuring out its idioms on my own.
Despite all the struggles, I finally see the light and I'm starting to understand why Rendr is so powerful.
tl;dr - If you're willing to source dive and figure out your own workflow, I would suggest using Rendr. Otherwise, I would recommend going old school by writing a traditional client app with a more mature library. (is it too early to say that? =X)