Just my two cents: I'm currently building an app on the Shoutem platform, and have been required to extend one of the Shoutem extensions to do so. I have been in direct communication with the Shoutem team throughout this proces, and have gotten to know the platform intimately.

A month into it, I can honestly say I can't recommend using the platform (yet). While the idea is an interesting one, it's bloated, buggy, slow, and doesn't offer much over optimizing a website for mobile devices. That said, the team behind the platform is great, and I'm confident they'll work out the kinks over the coming months to make it more user/developer friendly.