This is one is a lot cheaper than the ones I've been looking at, which is great

I do have a question though. For the products page,
Pup-Pads™ Reusable Absorbent Pads, do I need both the absorbent pads and the absorbent tray liner? Are they the same thing? Is one better than the other?
And is this whole thing better than washable pads alone?