Alexander, I have horn hooks on about half my fleet here. I like old time steam, my kids like modern diesel, and most of the modern diesel locomotives, freight cars, and passenger cars have horn hooks, while the old time steam locos and cars are all Kadee or similar. Mostly, this is because this is how they were when we bought them.
When you sit on top of a boxcar, looking towards the front of the train, the horn-hook’s spring is pushing the coupler to your left. The car in front of you has its coupler spring pushing to your right. When you couple them together, there is a significant force pushing the front of the car you’re sitting on to your right and the back end of the car ahead of you to your left. Now, this force isn’t strong enough to knock over either car, but once you get them moving, and they encounter rough track, or a turnout, or any other problem, then the sideways force is the straw that breaks the camel’s back, and the horn-hook cars tend to derail first. Backing up, you are using the coupler to push with and that causes problems also.
Eventually, all the cars and engines that stay in service here will be switched over to Kadee couplers, usually one train at a time. The plastic copies of the Kadee coupler’s will be replaced as they break, or if they refuse to uncouple properly over a magnet, or if they start uncoupling when they aren’t supposed to.
I bought one of those Wal-mart organizers for the shop here, a plastic box thing with about 20 slide out drawers. Couplers occupy one whole drawer, while coupler boxes occupy another one. I bought a big bag of Kadees, 20 of them I think, and a couple bags of Joe Somebody’s Universal Coupler Box, a Kadee coupler height gauge, and a bag each of 0.015" and 0.010" shim washers, and now, when ever anything coupler related breaks, needs swapped out, or fixed, the tools and parts necessary are close at hand.