I have been using Samsung Gear (first version) for almost two years with firstly Galaxy S4 device then switched to Galaxy S6.
Found it very useful, especially when you are attending meetings (keep your phone silent, the Gear will give all notifications), while driving you can also answer the call since Gear has built in speakerphone.
Quite useful when doing some hands on work with both hands busy. It got a nice camera as well to take pictures / videos. Also has pedometer, counting your steps as you start a walk. Battery life is quite good, it gives me full two days backup (of course usage dependent.).It has voice commands, you may call a number while driving using voice. There are good apps available but I didn't try any.
For me, it's not few days fad, it is actually useful for me. Never gave any problems, just keeps working and doing its job.
Finally, if you forget your phone and walk away, it will remind you. Also if you forget your watch, your phone will tell you. I saved my phone at least twice.