A while back I decided to try MIT App Inventor to develop a mobile app for Android. The goal was to send sensor data from multiple soil moisture and EC sensors to smartphone over Bluetooth Low Energy (Bluetooth LE). The result of that project was the SHUSHAN Mobile app that was available on Google Play until recently. When I started the project, it was with the intention to just get my hands dirty with mobile app development, but then I continued using the MIT App Inventor and was able to develop professional looking apps.
I have explained the details of the app in the blog article below: Sending Data from Multiple Sensors to Smartphone over Bluetooth LE (Part 1: Open-Source Mobile App)