I have three of these lenovo devices setup around my house doing on-device wake word detection, but they use a 3rd party app plugin that runs snowboy for the actual detection, not openwakeword. Despite the 3rd party plugin the experience is pretty fast and seamless, though I think your method has a few advantages, such as working on earlier versions of android, and being able to use openwakeword.
Here’s a video of one of mine in action:
See more here if you’re interested: Setting up a 100% local smart speaker on an Android tablet using Tasker and Snowboy to handle wake word detection