Anyone Use a Tracking Collar on their Dog?

[Travelover]

I'm thinking of getting a tracking collar for my dog in case she gets lost. There are two basic kinds. One is for field use and has a GPS transmitter on the dog which sends a signal to a transmitter that the owner carries. Range is about a mile or so based on terrain. The second kind is a transmitter that uses a cell phone signal to report location back to a web based tracker. This is the kind that I'm interested in, as I live in an area with good cell phone coverage for miles and miles.

So my question is - has anyone used one of these devices with any luck?

Example of the device I'm looking at:

Costco - DogTracs? GPS for Dogs Member Service Plan Discount Included