From the manufacturer:
The ME-302 Micro Educator 2-Dog couples our most popular Transmitter, the ET-300 Mini with two all new RX-070 Micro Receivers for small dogs. The RX-070 is an all around smaller version of the RX-090 Mini Educator Receiver at approximately 20% smaller, 20% lighter and 20% less stimulation. And for even more small dog considerations, the contact points are approximately 20% closer to one another and the collar can be turned 90 degrees on the strap for a "fore and aft" contact point position rather than having the contact points going around the neck. Like the ET-300, it is still rated for dogs 5 lbs and up, but the newer configuration allows for more options when fitting it to a very small dog.