Unethical? People who want a horse but for whatever reason are not ready to own one can rent/lease one - happens all the time. In face they are rented by the hour every day.
Wouldn't it be a MUCH better idea for people to be able to 'rent' a dog for a month or two before buying one? They would know exactly what they're getting into before hand and the eventual puppy/dog would be the one benefiting from it.
Personally I wanted chickens for about a decade before I finally got them. What was holding me back? No coop. That was it. I didn't have a coop and had no idea how to build one. If this had been an option for me, I would have probably gotten over my fear and uncertainties many years ago.
I think it's a brilliant idea and a great way for someone who is able to toss together a few tractors to make a little extra money.