I was up by Great Falls, Montana a few years ago, when they were celebrating the Lewis and Clark expedition, and made a side trip to the museum where you could try throwing darts with an atlatl. It wasn't nearly as hard as it looks, and the easiest one for beginners was made from what looked like PVC plastic pipe. I favored the Basketmaker design which is made to be held between the first two fingers instead of in the fist. Uses more arm and less shoulder action, which is good for me, the aged, and the lame.
I didn't see any mention in your source, but atlatls are stored energy tools, the same as a bow. If you launch the dart with enough gusto, the shaft loads up under acceleration, and releases it when the dart is released.
Above all, the experience was plain fun.