I looked at them a while back but never pulled the trigger. They couldn't hurt but I'd get the one that swims back and forth instead of the ones that twirl in a circle. The "paddle wheel" models I believe look the best.
Like you said though a jerk rig works and it's simple and cheap.
Like the concept, but if you hunt more than 10 times a year they won't hold up. We sold all of ours and went back to pulsators. They are heavy and a PIA to charge every night, but at least they hold up.
any motion is good motion......unless late in season- see how fowl respond and act accordingly......dont over analyze. if you have food and water you will have ducks- higdon bubbler very good as well- used them for years- have both