Buying a small car trailer can be good reversing practice but un-needed.
Generally speaking, if you are buying a tiny little trailer half the size of the car you will struggle reversing it. Because reversing a car trailer is much harder then reversing a hgv trailer.
This is because the car trailer is a lot smaller so it will jack knife while reversing very easily.
For a cheap way to practice reversing I would recommend Euro-truck simulator.
store.steampowered.com/app/2273 … mulator_2/
Costs like £15 on PC. There are similar games on PS4/Xbox.
Good thing about the PC version is it has a free demo.
At a yard I worked at we had a van with a tiny little salt spreader trailer on the back. The majority of the drivers could not reverse it because they could not see it in the mirrors. The only time you could see it in the mirrors was when it was about to jackknife. Most people just un-hitched the thing and pushed it in the bay as it was just easier.