I have two older units. A Lowrance fixed unit (5 channel) and a Magellan hand held.(12 channel)
The Lowrance is easier to use in my opinion. The handheld eats batteries very quickly, so I usually use it
with the lighter socket adapter in the truck or on the boat. I guess an ATV could have a socket to plug it in, but if you're lost in the woods on foot, two AA batteries last only a couple of hours.
We had a smaller boat that I wanted to use the Lowrance/GPS with.
I rigged a board with the fixed unit mounted to it, GPS antenna included.
Another narrow board has the transducer and speed/temp. mounted on it.
This gets clamped to any boat transom and you have a portable sonar/GPS,
provided there's a 12 volt battery to connect the power wires. The whole thing
fits into an old milk crate for transportation.
Not the most sophisticated looking set up, but it's worked O.K. since the early 90's.
I even took it out ice fishing when we had a snowmobile and sleigh.
Didn't have the hand held back then.
Good luck with your choice.