I do that "all the time", as I have R compound tires on my Boxster.
Yes, the u-haul "car transporter" is no a "feather light" trailer, it is a heavy (duty) one.
..and the risks that it would "take off & fly" are quite reduced, even at high towing speed !
Sure, the ramps are not the longest ones, so, to ramp up my Boxster (that has PSS9 on low position !) I do few tricks : one, I have a pair of RhinoRamps (60 bucks) to back up the rear axes of my towing car.
My towing vehicle is a CTT, so, I also set the suspension to high "terrain mode" (to load/unload).
The loading and unloading of my car is piece of cake, with the length of the u-haul ramps.
I also have two pieces of "mini ramps" that I drop in the front of the trailer, i.e.: to be under the front wheels, in order to left a bit the front lip spoiler, in order to not hit the front of the trailer with the spoiler.
The good : you do not have to have a spot to store your trailer, you have no insurance nor DMV to think about. The other good : The u-haul guys connect and de-connect the trailer, you keep clean hands, (while watching them !)
The cons : it cost you (I take normally two days) about 60 bucks a day, and you have to go and pick-it up and return it. You cannot open the doors to get in/out, but, as I have no roof, I use the same technique as entering/exiting a bathtub. If you have a roof, you can pivot the trailer wheel protection/cover, and this should let you open the door.
About the attachments : (provided by u-haul), in the front around the wheel both side, and one chain that sometime, when it is long enough, I connect it to the tow hook, (it should provide a psychologic help !) and in the rear, one chain, that "sometime" I connect, around the rear attachment of the anti torque bar, (quite easy), but, frankly, if you have a problem that would require that this chain is needed, I think, it become quite "secondary" !!
About the brakes : in my case, the CTT has brakes that would stop a freight train, so, it is really all fine.
I have a boat, that is not that long, ..but fat and heavy (it is a Cobalt), and for that, we do have a trailer (all is parked/stored inside a closed garage in marina), and the whole things is over 6'000 pounds.
In that towing case, I can say, then, that one, I *do* feel it, but a Boxster (ok, mine is light
i.e.: no roof, li-ion battery, light seats, light wheel, etc..) ..I simply do not feel it at all.
Even, sometime, looking at the mirror, I think : "who the hell is tailgating me that close ??" to realize and .."sh... I forgot that I have the trailer down there !"
Note that for u-Haul, the "car transporter" is not always available, I recommend reservation as in advance as you can. Because if you have to get one from another location than the nearest one, ..you also have to return it there, ..if you want to avoid an heavy surcharge for returning it to a different than pick up location !
I hope that with the above, ..you got it all !!
A view of the little front wood ramps, to have peace with the spoiler lip : (note that I do not two with the top cover, I just need it, as ..I have no roof, to gain 18kg !)