I am a geek & have a few Garmins
The most recent addition is a Forerunner 305. The Edge 305 is very similar in functionality, but is designed with a bigger display and is more bike centric. It does have barometric altitude which is more accurate than the Forerunner's GPS based altitude. So, if that's a feature you are keenly interested in, the Edge is a better solution.
Both have cadence options.
The HR strap is very comfortable, it's a bit softer than the hard polar strap (Polar makes a soft fabric strap also, I have no experience with it). Both it and the wristband on the Forerunner are just adjustable enough that they fit me (smallest possible on both). The watch part does look big, but it does not flop around (which would drive me crazy and be a deal breaker).
As mentioned, data's uploadable to MotionBased, which is pretty cool, and it also comes with a Garmin app if you don't want to use MB. I use TrainingPeaks so I just send it to that. Anyway, it's really neat to see the graphs of your HR data, visual course etc. But I am a geek so playing with computers and data is in my nature.
You'd be able to set the fields, there are a couple of display pages you can tinker with. You give it your HR profile, bike profile, etc and it will let you tweak the zones it creates if you so desire. In all, it seems to be very robust functionally. I have had mine for a week and used it outdoors 2ce running and indoors 2ce biking (trainer).
Battery: is said to be ~8 hrs for Forerunner, 12 for Edge. I will be using mine this summer on some multi-day events so I will find a battery pack to charge it overnight. I got the Forerunner over the Edge because I wanted to use it for multisports.
Also, the Garmin appears to store indefinitely old data, and the manual says it stores like 2 yrs of data. Of course, you may not want that much. You can go in and delete it if you want, or just let it fill up and it'll overwrite the oldest when full.
You can see the manual here:
http://www.garmin.com/manuals/967_OwnersManual.pdf
I don't think you'll be disappointed. Garmin is a great company and they have (from what I've heard via others) excellent tech support. I've never needed it for any of mine, but I'm glad they have that reputation.
It will take a minute for your GPS to acquire tho, so be sure to turn it on while you're still organizing and getting ready to go.
Edit: I should add that it is not at all like a car GPS in terms of Nav - think of it more as a training tool that allows you to know a lot about where you went rather than where you're going. If you do a usual ride you can use this as a measurement of your progress over time. As far as nav, you can mark waypoints (locations) and build routes from them, but it won't really tell you how to get to the nearest Starbucks. Hope that helps a bit.