Another advantage to the strap-on carts is you can locate them wherever you want on the boat.
With the Hobie standard cart I can't fully load my i12 until I launch. I fish, so most of my weight - crate, tackle, rods, cooler, etc. - is going in the tankwell behind the seat. With the cart under the mirage drive well it means I have to load everything near the mirage drive well or the weight distribution is too ungainly for anything put REALLY short hauls.
It would be much better to put the cart wherever the best balance point is.
I'm looking into the Wheeleez carts for this reason.