I only ever bought 1 in the LPS and while it was free from pee it just made the worst mess once the connector hay peices frayed. I didn't really like them. I might get one for Acacia's Gotcha Day in January. We'll be moved into our own apartment so it might be easier to clean (no carpet!! I'm so excited!)
I love the grass mats. My boys will spend hours ripping them up. On the downside I think that might have been where they acquired their love for chewing up spots in the carpet.
I've gotten grass mats for my buns before and none of them ever seem interested in them. Jabber actually prefers the carpet I got him, he doesn't chew it up but lays on it.
The chinchilla, however, adores the mats. She just loves ripping them up!