Simple tip, if you need to test MQTT related projects with your PR-1 without running Mosquitto on the PR1 (risky) or using a PC? I have used and old motorolla G4+ cell phone android 7, running the app Termux (linux terminal emulator) in order to run Mosquitto in the device, the PR1 nodered receives the data with no issues and I have performed intense testing and integrated with several devices. It works perfectly even with heavy loads and the built in battery gives me a lot of flexibility not to mention that you can also check on Groov view on it. I removed non needed apps and services and the device works flawless serving data to the PR1 from several wireless movement sensors and shelly 1 devices.
I will not try critical applications but for testing and non critical I got surprised with the new use for the outdated cell phone as a server/HMI interface.