This is the amount I got from a single diaper. Its about half a liter.

as the article correctly states, not all hydrogels are made the same. the ones in diapers and menstrual pads are specifically designed to NOT rerelease absorbed liquids. there are other hydrogels out there which are designed to absorb and dry out repeatedly without degrading or losing absorbancy, and are therefore more suitable for plants. i dont have any deeper experience with hydrogels, but I did have it as a consideration for my kratky (passive) hydroponics setup.

I’ve used what are called tree diapers which I assume are similar. They do seem to help for sites that won’t get enough water. Personally I don’t see a need to use them for potted plants but if you are struggling to remember watering them I could see it.

I do like laid back gardener, their information usually is solidly researched so I trust their opinion if they are skeptical.