that first one seems like a pretty good one. even with the installation instructions right there to plainly see. drilling holes isnt too big of a deal if you follow the directions, measure twice...etc. just be very aware that the "weight carrying capacity" is 500lbs less than class 1, and that max tongue weight is less than most people.
that being said, using just a ball on the bumper would work for very lightweight stuff, and really low tongue weight.
how big is this boat?
its fairly reasonable to assume that at some time you will overload whatever you're pulling and what you're pulling with. the bumper ball would probably fail less spectacularly, but would be more likely to fail (methinks)