we use these for our 19 year old cat as she will rather go on the curtain than use a litter tray ;)
she has a medical condition that will make her drink (and pee) a lot and we use these as her exclusive toilet (though not happy with the waste we produce we haven't been able to come up with anything else yet).
since we have to use these days in and out ( 4-5 per day) we try cheaper pads every now and than (in the hope of finding something similar in quality but cheaper in price), so far without luck.
these seem to contain some sort of moisture absorbing powder (a bit like those water retaining granules you can get for plants), i accidentally left one out in the rain before and it swoll up to 5 times its normal height, whilst still retaining the water.
all the other pads seem to be just a layer of paper towel material with plastic underneath and as much as we'd like them to work they are nowhere near as good and absorbent.
if your cat likes to go very close to the edge than the pad not being well absorbent will result in a "puddle" on the surface and the pee running off the pad and onto your floor. the cheaper ones also tend to feel as if the underside is not fully water proof.
very happy with these, but wish they could be ordered on subscription. price was hiked up by nearly 10% since last order too!