I have 2 tow dollies with disc surge brakes, I've towed cars with them a good many miles, and they have worked flawlessly over the last 15 years. The surge brakes apply, and disengage much smoother than electric trailer brakes do.
When you would be in an emergency situation, you take your foot off the gas, and immediately the surge brakes start to drag. If you start braking the tow vehicle they will apply proportionately. I own a lot of trailers, and I actually prefer the surge brakes for towing over electric.
I also have driven 18 wheelers hundreds of thousands of miles, the air brake system on a rig is also a much better system over electric. In the years I drove tractor trailer, in all kinds of weather, I'll bet I can count the times I've used the trailer brakes independantly on one hand, and still have fingers left over. Any system that is well engineered proportionately will keep the trailer in the back, where it belongs.
The worst case scenario is a trailer without brakes in an emergency situation. I have a few light duty trailers (under 3000 lbs.) those are the ones I leave plenty of room in front of me. I have K3500 dually, and I prefer to haul my trailers without brakes with that, rather than a car. Just because I need as much braking power on the tow vehicle as possible, due to the trailers having no stopping power, and wanting to shove the front vehicle in a quick stop situation. Towing a tailer with no brakes, loaded heavy, with a light tow vehicle is the times I get my sphincter exercised.............
U Haul rents to anyone with a credit card, drivers license, and a tow vehicle, so their stuff is pretty idiot proof. They never even ask you if you've ever towed a trailer previously, take that for what it's worth...........
