The human powered one I showed was EXTREMELY effective, and the donkey powered ones probably even more so (a donkey is heavier and stronger).
There was a TV series on in the UK a couple of years ago, where they were given simple drawings (often very vague and very old drawings), and had to try and build a working replica, improving it if they could. One was a medieval multi barrel cannon (which worked really well) and another was a human powered crane.
They made space for two people in the 'hamster' wheel, and improved the design by having two gears, and a swinging jib - they easily picked up a car with it, and swung it round to drop it elsewhere.
You tend to think that losses would be huge, but such devices work, and work well, as do old water wheels and windmills. When you look at the size and weight of them it's incredible that they can be moved at all, never mind provide power from a relatively small source.