I bought one of these as I've just got into cycling and running and love tracking my fitness, routes etc on the forerunner. I found it a pain using the forerunner on my wrist when cycling as I kept having to lift my arm off the handlebars to check the metrics. I also found the strap to be a little uncomfortable on the rubber strap which comes by default with the Forerunner 305, however with this quick release kit both my issues have been resolved.
The quick release kit attaches quite easily to the handlebars of the bike with two cable ties (supplied), this gives quite a secure fit providing you tighten up as much as you can before trimming the tie down to size.
In order to be able to use this release kit, you need to remove the normal rubber straps from the watch and you replace the pins in the watch with the new ones supplied. This is all very easy to do as Garmin provide a simple tool in the box. It takes no more than a minute to do this and isn't really that fiddly providing you don't let the new sprung pins jump off on to the floor where you can't find them again (luckily you get several spare ones in the box too in case you can't find them :) nice work Garmin!).
Once you've replaced the straps, you can then use the included new wrist strap which uses Velcro rather than rubber with holes, this means you can get that perfect size on your wrist, and actually makes it a lot easier sharing the forerunner with my girlfriend who has much smaller wrists, as previously we needed to switch the straps each time to the smaller ones, when she wanted to use the forerunner. The velcro strap is also a lot softer and doesn't rub during long runs.
Switching between the bike and the wrist strap is all very easy thanks to the way the clips are designed.
A good piece of kit and I would recommend for anyone who both runs and cycles.