Yes indeed be cautious! On my AT&T L-920, I initially wanted to try the Windows 10 mobile 'Insider-fast track' trick to attempt to only get WP 8.1 Update 2..however this attempt failed, and 'fast track' updated me directly to Windows 10 mobile TP build, which was quite buggy...as expected not ready IMHO for daily driver use..Utilizing the NRST flashed back to WP8.1...within a couple of hours...but at least 'got to see new developing WP 10 TP GUI and features...