FWIW, about a year ago (maybe 2? who knows anymore 
) I moved everything I could over to S2 -- for me, that's currently 28 out of 30 ZW devices.
It's been a definitive win for me -- my mesh has never been better. The only gotcha is that the built-in ZW firmware updater doesn't work for S2 devices, but these update steps work great instead.
