I've been using Xamarin since mid-2012 and have developed a couple of niche imaging products on Android and iOS for my employer, plus some internal tools on Android.
Overall I've been very happy. Code re-use hasn't been stellar, but good enough to repay the investment. We have re-use not only between apps, but also between mobile apps, Windows desktop apps, and our application backends. I also feel I'm more productive than if I had so swap between Java/Swift/ObjC/Andorid Studio/Xcode.
Stability has improved a lot in the last year. Paid-for support was pretty good (esp. guys like @jonpryor), but the self-serve forums can be a bit hat-and-miss. I never had any killer bugs (but then I never used Xamarin.Forms...)
Overall I've been very happy. Code re-use hasn't been stellar, but good enough to repay the investment. We have re-use not only between apps, but also between mobile apps, Windows desktop apps, and our application backends. I also feel I'm more productive than if I had so swap between Java/Swift/ObjC/Andorid Studio/Xcode.
Stability has improved a lot in the last year. Paid-for support was pretty good (esp. guys like @jonpryor), but the self-serve forums can be a bit hat-and-miss. I never had any killer bugs (but then I never used Xamarin.Forms...)
Overall: 85% happy with Xamarin.