Purchased a Mini 300 for our new 9 month old pup to work on off leash training (using both a trainer and online guides, gotta do it right for it to work!). Love this collar so much, started using it with our older dog. Decided to get a 2nd collar, and sent a message asking about details about combining collars vs getting a 2nd set and all the technical details behind how they can work with 1 or 2 remotes. Got a response the same day with in depth answers to my questions! even fast responses to my follow up questions! Online right now to get a 2nd one for our older dog, that is well trained, but these work so great, it makes her incredibly consistent with recall while we're out hiking in the woods!