I started out with the MR300 (the small one for personal use) and have used it extensively over the last couple of years. As explained, it works well for your immediate area when you're stationary, and helps a little bit while you're mobile.
If you sit for greater period of time, like crappeeeman, or me now thanks to injuries, then you'll appreciate the Patio Shield model that offers a 15' zone of protection.
If you're in a boat, I can't really comment as I have no experience using it in a boat as I don't have a boat.
I used my Patio Shield model when I went out for walleye earlier this year and not only did it work for me personally it protected a friend who was 10' away from me. Not even a bite....except for the fish.
Patio Shield Mosquito Repeller