Cushioning that reduces impact load.
Knee pain has many causes and most of them are not footwear. Shoes are worth considering as one contributing factor, not as a fix.
Where footwear plausibly helps is in reducing the impact travelling up the leg, and in correcting excessive inward roll that changes how load reaches the knee.
Three shoes at similar prices built on completely different ideas about cushioning. Only one is a genuine distance trainer.
Stability shoes aren't all the same. Modern guided designs and traditional medial posts solve the same problem in very different ways.
Three On shoes that look similar and are built for completely different things. One of them isn't a running shoe at all.