I have a Koplin and it worked just fine, but I can also put my rifle across my shoulder for the short trips I normally take. The Koplin boot makes a darn nice airline case, and I prefer it to any other model I've ever owned for shipping a scoped rifle.
Never taken my ATV anywhere that I needed a GPS on it. I have needed a GPS to find my ATV however. When dragging a deer, it is very helpful to know the shortest route back to the ATV when the woods is too thick to take the ATV to the deer (normally the case in Eastern NC).
An older fellow no longer in my club, had every accessory imaginable on his ATV. He had so much crap on the front and rear that there was no way to put a deer on it, which is the reason he owned it to start with. He looked more like a soldier than a hunter. Victim of too many mail order magazines.