I've been using a Garmin Alpha for almost 5 years. I can't imagine going back to a non-GPS collar!!!
That being said, the remote control on the Alpha is kind of annoying. Not very ergonomic design, the touchscreen is constantly getting "touched" and on some wonky function while in my pocket or being carried on it's leash. The touchscreen is also easy to scratch, so I would REALLY recommend putting a replaceable screen protector on it as soon as it comes out of the box. I had to cut one down to fit from a phone screen protector, but it's still on their and working as intended.
Overall it's a good system that can be expanded to multiple dogs, I'm just not a fan of the remote. Oh yeah, and the collar's antenna is long enough for the dog to chew on it.