We are using Vapor to drive our app backend and have been using it since the tail end of version 1. It's been everything you would associate with young technology, a fair few painful moments (especially migrations from Vapor 2 to Vapor 3), but the joy of writing Swift on the backend and sharing code between our app and server has been a pleasure (sharing model and endpoint descriptor code between platforms is great).
Would I recommend Vapor for a serious production environment?... yes and no. It has been a huge time sink for us when API's have drastically changed from one version to another, but I feel like that 'should' be stabilising now. Also roadmaps and documentation are a very light in areas so its very difficult to anticipate what's around the corner and how best to prepare for those changes unless you are really deep into the community. If you are prepared to spend a bit more time on a vapour app then it will reward you, but if time is of the essence then for now maybe look for a more established technology.