I have a Garmin Alpha, it's the GPS version that tones the remote to let you know when your dog is on point. Basically, it lets you know your dog has stopped moving.
It's a good to great collar system, has a vibrate feature for communicating with the dog when you don't want to shock him. Only two negatives are, 1. the antenna on the collar is ridiculously long; and 2. the screen on the remote is plastic and you will absolutely want to put on a screen protector. I cut down a protective screen for a smartphone and that has served me well.
The cost of the system is not trivial either, about $600 for a single dog setup the last time I looked.
It's worth it though, I used the GPS feature on the collar to setup a perimeter around the yard to let me know when he leaves the area. After a few weeks of working with him, he no longer goes out onto the highway or over to the neighbor's place. Wish I could say the same about his fricking lab.