my supra was on a single axle(30 miles each way x 18 trips/yr x 5 years of ownership and never an issue) and the mondo I rode in wisconsin was single as well. it's WAY easy to move a single axle around if you have some garage issues or space issues that make hooking up or storing a challenge. I can't even budge the dual axle my last boat sat on.
if I was towing a lot I'd opt for the dual every time. if you are not towing much, close to the ramp, or you have some tight confines to store the boat in, single is sure a lot easier to manipulate and the mondo really doesn't need a dual.
a lot think that you HAVE to have a dual axle but I trust the engineers at boatmate that they know what they are doing and IMO in some cases it really comes down to someone wanting a dual axle "look" not necessity for the boat.