I'm considering getting myself a sling trainer, after I was able to try one at a gym.
I found one major difference between cheap ones, and expensive ones (as the one on the gym), which is the wheel, which makes the string between the handles move really easy I guess.
Here is one without wheel: (Product)
And here one with wheel: (Product)
I'm thinking, the wheel is important and in order to get the full effect of a sling trainer I should get one with wheel, but before I put the order I'd like to get some input from some more experienced people.