Arielette ball has more holes across top than Downy thing. The latter is just a ball with a stopper or something IIRC. During spin cycle it would be thrown against side of tub which caused it to open, contents then would be dispersed during rinse.
Of course Downy ball was meant to be used with top loading washing machines American households favored at the time. Thus there was copious amounts of water to flush out (hopefully) contents.
All this came about because few top loading washing machines then had fabric softener dispensers. So people had to listen or otherwise look out for start of rinse, then run to machine and add FS. That or return after machine had completed cycle and restart for another rinse.
Dryer sheets were invented and largely supplanted liquid fabric softeners for this reason.
There were early attempts at fabric softeners one added to wash cycle (Rain Barrel), but they were largely useless and soon vanished from market.
Next attempt was using clay (bentonite) which gained a bit more traction and was found in "2 in 1" laundry detergent/softener. Clay is also the active ingredient in those in wash fabric softener crystals flogged by Purex and others.