My observation has been:
Is the LoRaWAN stack buggy
Not as far as I can see. Some issues around sleep modes, but they are documented.
or feature complete?
Yes, but my experience had been with LoRaWAN 1.0.1
Is there support for the AU regional parameters?
Is deep sleep effective for extremely low current draw?
Haven’t tested current draw but am happy with the results I get
Is it easy to wake from sleep periodically?
Yes. Hardware Interrupt or RTC
Is the mbed learning curve steep or can most of it be stripped out?
Pretty easy if you start with their working examples
Is the dev environment, including programmer and IDE,
Under $100 for the basic programmer. IDE is free.
Harder than Arduino, simpler than Eclipse
I’ve had issues with the online environment, which effectively meant it was down for a few hours.
You can use mBed offline components as well if you prefer
Is it easy to sample a couple of analog channels,
including battery voltage?
This might be a bit harder, since (I think) analog inputs will be represented as a percentage of battery voltage, so you’ll always read 100%. There might be a constant voltage source on the MCU that can be used. Somebody with more experience than me can probably correct my comments.
Is it easy to commission individual units with unique ids and shared keys?
Yes if you have the same AppEUI and AppKey. (But note potential security issue of sharing keys between devices).
Is it easy to interface to a battery supply?
Yes, see specsheet for details.
Is it easy to mount the board in a custom enclosure and attach an antenna?
Easy enough, if you buy the version without header pins.
Is radio performance satisfactory?
As far as I can tell