I just last week reset my phone for getting a new 15254.401 update. I can not get it (maybe) because I'm on the insider ring..
Your question: After the reset I installed 6tag to 640 LTE Dual SIM again. It works fine, still. I have Fall Creators Update (15254.369) on my 640. The 6tag app is on the phone memory, not on SD. There is also Instagram for Windows 10 Mobile available, too.