While still waiting for my Astro, FWIW, I'm using an Adonit Dash 3 with my Cosmo. That's an active capacitive pen, essentially emulating a finger, but able to have a finer tip (2-3mm) thanks to the active electronics making the signal stronger. Compared to an active digitizer pen (think S-pen), it's pretty crappy, but works without any special digitizer hardware in the phone.
The Astro stylus should be pretty much the same thing. I backed it anyway. One could argue that using the particular model Planet tests with, might, within the limits of the concept, make it work as well as possible, but - honestly - I was mostly curious and had the money to spend. Once I get it, I will likely compare it to my Dash and post my findings on this forum.
