I've got one of those, and I like it a lot. I've seen bad reviews, but mostly people seem to be complaining about inconveniences like having to hit a button to get it to start. The altimeter is cool, but it's mostly useful for relative altitude. I never take the trouble to keep it calibrated to absolute altitude because you have to reset it whenever you drive somewhere with the bike or even when the weather has changed since your last ride. The altimeter records every little bump you go over. Don't be surprised when your cumulative altitude gains come out as much as double what you see for the route on sites like MapMyRide. I think it's just because those sites are just sampling altitude at various intervals along the route and miss a lot of rollers.
If you don't already have a cadence sensor and would like one, check out this eBay listing:
Motorola Bike Speed Cadence Sensor for MOTOACTV | eBay
Because the Node 2.1 uses ANT+ for connectivity, you can hook up sensors from other brands. I'm using the Motorola one above and have had no problems. I would even say it syncs with the computer easier than my original Bontrager speed sensor did.