You have to take the tour with them. You can't go out on your own with the trikes. You can rent just a Harley for the day but if you really want to see the Island, you need a 4 wheeler or a Sportsman 4 wheeler so you can go off road and explore.
Snorkel Mangel Halto, day or night with a waterscooter. Check out our website. E-mail Stuart at firstname.lastname@example.org or call Stuart local: 745-7459 Or visit: www.arubabobsnorkeling.com 47th trip in June 2015 and 48th trip in Nov 2015.
We rented Harley's from the Harley Dealer a number of years ago and it was a blast. I would say that you can almost see as much of the island on a bike as you can in an economy car, but like Kent stated, if you really want to see the innards of the island some sort of 4X4 is your best choice. You could certainly experience the Harley ride for a day and then venture off to something else. Keep in mind that the sun is intense and the tragic can move slowly most of the time, so it can be a bit warm, but that's part of the Aruba experience!