I used App Inventor before learning about B4X environments
Also creating apps of discrete complexity and size
But some features are not present, for example the realization of services or operations in the background is not possible (or rather a couple of years ago it was not possible), besides the accurate debugging of procedures created with App Inventor is extremely complex. and tiring, substantially based on the writing of variables dedicated to debugging or displaying these, in fact there is no concept of breakpoint or in any case of interruption of the program flow
Those two things, lack of service and extremely inefficient debugging, prompted me to look for other programming environments
The fact remains that App Inventor, equipped with all the available plugins, remains an excellent working environment to fully understand what the programming activity of an electronic device wants to be.
And periodically I return to have a fond look and leave some messages to the "code colleagues" with whom I have shared a small part of my professional experience.
Unfortunately for App Inventor, B4X systems aren't beaten by anyone