Does anyone know why one would choose Series 2.5 over 1 or the reverse? The Digi website is so covered in market-speak I can’t seem to figure out what the differences are. 
Series 1 is based on Freescale’s 802.15.4 chipset and MAC firmware.
Series 2 uses Ember’s MAC and some 3rd party’s chipset (co-developed). Series 2 originally was intended for ZigBee stack applications ONLY. And conversely, support for the ZigBee stack in series 1 was reduced or eliminated. (This shift is rooted in T.I.'s acquisition of Figure8 Wireless who had been the ZigBee stack provider to Freescale.)
I’ve read that 80% or more of the 802.15.4 applications don’t need or use ZigBee protocols (often, no need for meshing); they just use 802.15.4 MAC addresses or they use a wireless serial port extension protocol (Hayes AT commands) that Maxstream provides.
Thus, if you don’t need meshing, I’d recommend use of Series 1. I suspect but don’t know that Maxstream has offered the wireless serial port extension firmware for Series 2.
Also, consider whether you want XBee or XBee PRO, the latter having 60mW or so rather than the 1mW of the non-PRO.
I’ve used many Series 1 for a long time had have been very pleased.
Thanks. It sounds like S1 will work for what I’m up to. The mesh stuff sounds cool, but I don’t really need it right now.