I will be using the "stick" in teaching environments over the next year so I have started compiling notes on how well it works with various hardware add-ons. At the moment I have a starter list posted at: http://tinkerfarm.net/projects/the-m5stickc/m5stickc-hardware-accessories/.
I will be adding to that page as I get deeper into it, next up will be some of the commodity sensors that people use with Arduinos, since my site is aimed at beginners. I hope this might be helpful to some of the people on this forum.

Nice work. I have the first three hats and waiting on the next set of hats but not had time to test them. I have been able to UIFlow to work with the temp/pressure and humidity part of the env sensor but I have had to put on hold testing will I go back to writing up and test all my old stuff first.
You can see my work in progress nots for UIFlow in the project forum.