Old thread, I know. Just paying an occasional visit to the forum.
XT1 - Great bit of kit. It has a couple of issues - with routing under some circumstances for imported routes (Ie - sent as a gpx file from outside, or from Basecamp, or anywhere), and with 'lost' data when using the SD card. Both of which can be easily worked around when you know about them.
XT2 - currently sending reports in to Garmin. Works perfectly without the Tread App linked. Better than the XT1 in my opinion. But once Tread is installed there have been reports of issues with BT links. Certainly after a phone call, I have seen the BT conenction for nav instructions, music, headset, and a second phone call have been disabled. After a few minutes it sorts itself out by disabling connections and re-enabling them. But the big issue for me is that it alsters the route and moved shaping points with it. Both issues reported. Still not resolved.
Without tread - neither of these happen - but you loose the traffic and weather data.
Which am I using ? I'm sticking with the XT2 for now. But for a well planned long tour in unknown areas, I would not be able to trust it without having backup plans. My experience is that it will get me to where I want to go, but not necessarily on the roads that I want to ride. They have just brought out a handlebar controller for it. Not yet ready to ship, but coming soon ! But oh so expensive.