I second your concept of Right tool for the right job but IMO using something that has massive boiler plate code, HandlerThreads seems fairly unsafe (looking at those hidden bugs which get lost between multiple threads like something from the matrix) and definitely a long time to code it. Yea Rx has a vertical climb to grasp the concept but once you do it, the async processing is definitely easier.

Do you use HandlerThread in any of your production apps?