The fetch is a great little device, great quality and small as it is, fits on my keyring and attached to my keys, goes everywhere with me.
Fetch was easy to pair (via Bluetooth) to my HTC One Max and is easy to use. I mainly use it as a camera shutter button (which is very handy for taking group shots with me in them) tho most will probably use it as a means to find their keys or phone if they misplace them. You can make the fetch beep from your phone find those missing keys or also to find the phone too. When paired, if the fetch and your phone get more than 15 feet apart the fetch will beep to let you know at a volume that is more than adequate. The only advice I would give is to make sure you switch the Fetch off if not in use for long periods of time. I accidentally left mine on for a few days and the battery depleted quite a lot, luckily tho the watch type battery that powers it is inexpensive and easily available. All in all a great device and well worth getting if you are the type that regularly misplaces your phone or keys.
To find out more head on over to HTC.com: http://www.htc.com/www/accessories/htc-fetch/