Brian, the above responses are spot on. I started with the Astro system by Garmin and my two older dogs started out with that system and also had separate correction collars for "just in case" they didn't listen to me. I upgraded a few years ago to the Alpha series which had both correction and gps functions in one collar and remote. As noted above, switching the "lock" feature on and off to access the correction mode is not something you'd want to do if your dog was speeding towards a road with an oncoming truck. If the unit isn't in lock, the handheld will go nuts in your vest switching features. I used the training feature on the latest addition to the MuttPak, a now almost 3 year old French Brittany. Differences between the 200 and 300: brighter screen and 55 hours of battery life compared with 20 for the 200. The "i" series is the Inreach feature which triggers satellite commo in emergencies for rescue or for texting when no cell phone coverage is available. As I carry a smaller Inreach MIni2 for turkey hunting, I don't need the "i" feature on my dog's remote. I still carry the Mini while dog hunting as I often hunt woodcock out of cell coverage. The "i" feature requires a subscription. Both the Astro and Alpha series bluetooth seamlessly to my Garmin Fenix 5 wristwatch with arrows pointing to the three dogs, color coded, and showing distances. You don't need the expensive Fenix watch; any of the less expensive Garmin watches have the same ability. When hunting, the remote sits locked in my vest pocket and I rely on whistles for correction and recall. A glance at my wrist gives me direction and distance. Garmin can't be beat for reliability and customer service answering questions about features. The Garmin collars have incredible battery life and feature a "lost dog" or rescue feature which extends battery life. This feature is controlled by the remote. My dog's location is updated every 2.5 seconds which can be extended to perserve battery life if necessary. What sold me on the Garmin collar was a trainer's account of "losing" a dog in the field that wouldn't respond to recall by whistle. The Garmin pointed towards a derelict barn on the property and she found the dog stuck inside the barn wedged between the exterior and interior walls most likely chasing a rat. Gil