I'm not a mobile app developer per se, I have created a basic Android app with only login capabilities / activity & fragment switching just for my own knowledge. However I've worked for a couple companies now that do app development.
My last company tried to use Xamarin for a while. They found that the documentation wasn't very accurate at times. They also found that they did not keep up with the newest iOS and Android versions at an adequate rate. Eventually they switched to native development for Android and iOS, with a shared REST api.
Take that as you will, I personally found creating simple Android apps to be somewhat easy. I didn't really know Java too well but the Android Studio IDE (Intellij) makes it very easy to pick up. I know nothing of Basic4Android, but I can imagine like other attempts to use other languages to build another language's apps, the implementation is likely not complete. At least in the case of Xamarin, the hassle of the framework outweighed the hassle of learning another language. And if you know one programming language, they generally aren't too much different.