I love the TinyPICO and use them in lots of my projects, and Seon is always helpful if there’s any issues. He’s put a lot of effort into this board and it shows.
I actually like the FeatherS2 for one reason, which is that it presents itself as a USB storage device and you can just drop Python files into it. Easier than the `ampy` stuff you have to do with the TinyPICO, and it comes with a "Stemma" port that you can wire up most Adafruit/Sparkfun sensors to. And it has mounting holes, which are a godsend if you want to make a proper 3D printed case for your project.
The only downside is FeatherS2 is CircuitPython and TinyPICO is MicroPython, and you don't get threading on CircuitPython.
Now that's really convenient. I'm creating a smartwatch with custom laser micro-projector, and would like to add such feature.