For the folks that have or are having problem with the S2 what exactly are you having problems with? I have the S2 and an older Sansung 8.4 inch tablet and have issue where the Go app will display the "Enter Device" button but will not show the "Go Fly" button. It doesn't happen all the time but pretty often. I found that by going into
eveloper Options" and toggling the "USB configuration" from "MTP" to "RNDIS" it would kind of reset itself and the Go app would launch and "Go Fly" would now be available.
So, if this is the same thing others are seeing with the S2 then you can try that and report back. In order to enable Developer Options do this:
Stock Android: Settings > About phone > Build number
Samsung Galaxy S5: Settings > About device > Build number
LG G3: Settings > About phone > Software information > Build number
HTC One (M8): Settings > About > Software information > More > Build number
Once you’ve found the Build number section of the settings, tap on the section 7 times. After two taps, a small pop up notification should appear saying "you are now X steps away from being a developer" with a number that counts down with every additional tap.
Brian