The I-pilot link can be linked to hummingbird depth finders and only them. The I-pilot cannot be linked to any depth finders so unless you plan on linking to your finders buy the I-pilot as it is a lot cheaper and has the same boat functions. 12 or 24 depends on your boat and how you fish. Buy the biggest you can afford and have room for the batteries. You can never have to much thrust or battery power.