It looks pretty neat - however - the proof is in the pudding - Try it and report back.
I currently run Mosquitto on my own server and am amazed at it's ease of use and speed and all the examples of usefor b4a, b4i, b4j and b4r are on this forum.
I personally use CloudMQTT, I highly recommend it. As I control my devices from outside of my house (I didn't want to port forward and send myself my IP address every X hours) it was a perfect solution for me, I also have my own MQTT server at home which I do not use. I actually have my own online server (I use for customer databases), I've been thinking about setting up an MQTT broker on there, but to date I've not had the time.
I have set up a MQTT-server (mosquitto) on a VPS and it's running without any problems for some months now. I have added the Mosquitto Authentication plugin as well. I have tested it sending audio-files and heavy attachments, which might not be the intended usage, and it is really fast. My VPS-provider is doing back-ups of my server so if something happens, I can quickly set up the server and services again.
I really do not see any reasons to use other third party services...with some "trial and error" you can set up a similar service yourself.