I've got the SE and am impressed so far.
Re airplane mode - iOS will let you run bluetooth with airplane mode on, in which case I think the iphone (i've only done it with an ipad) will use the GPS signal from the inreach. That said, I don't plan to take a smartphone, I found the onscreen keyboard on the SE was easy enough to use, and you can pre-write an unlimited number of messages on your PC first and download them to the device.
The cost struck me as very reasonable for the way I use it - $25/year subscription (on the "freedom" plan) plus $15 per month each month I need it (basically 3 months for ski touring and one for hiking). No activation fee on this pricing plan.
For my hike this summer, since I'm with friends and kids, I'll probably take the all-you-can-eat $65 package for a month and send/receive unlimited messages. This makes it $135/year, or $85 if I just take 4 months basic usage.
You can configure the tracking point interval from every 10 mins to every 4 hours (or off entirely). It also only sends a tracking point if its moved >100m so effectively goes into a low power/sleep mode at night.
