Heart-rate monitors units are fairly simple things. They strap around your chest to hold a couple of electrodes in contact with your skin to detect the beating of your heart, transmitting this information wirelessly to a nearby receiver.
The Garmin offering is no different in it's function. But it is different in a couple of other ways. The piece with all the brains in is longer than some other brands, making up "half" of the band that the complete unit forms around your chest. It's made from a pre-shaped soft plastic, with "ribbed" electrode pads built in. I've found this shape to be very comfortable, fitting neatly round my chest and staying in place with no bother. In fact it's so comfortable that I really don't notice I'm wearing it, even after 14 solid hours of cycling.
I use it with a Garmin Edge and have never had any problems with signal, it usually syncs with the main unity within 10 seconds. When riding in a bunch with some other users, it doesn't suffer from cross-talk staying paired with my own Edge and keeping my heart rate to myself.
The battery life is very good, I found that it needed replacing after maybe a year - during which it got used around 6 - 8 hours a week.
If I've got one gripe it's that Garmin went and invented their own standard rather than licensing Polar's. So until Garmin's ANT+ Sport standard gathers momentum it's unlikely that this unit will work with the majority of exercise equipment in Gyms etc where Polar still reigns supreme.