That's cool! I wanted to get an M5Stack anyway to play around with. A question about the secure chip: does the firmware actually recognize it is running on a M5 with secure chip & use it or is it not used? I mean, if it's not implemented, then having it on the PCB won't help.. 
M5Stacks are a great little devices and sometimes you can find them on discount deals for very cheap.Secure element is used for sure and if you watch the video on their product page you will see that it is used for encryption.
I never ordered this exact model so I didn't test it myself how it works in real life or as a hardware wallet, but you can contact their support team for more information.
I know that creator of Bowser wallet and LNURLPoS (arcbtc), is very active so you can also ask him if he can help you with this.
