Clay based cat litters can cause all sorts of problems. Litters made of small pieces can also cause problems both with ingestion, being quite uncomfortable, and with getting stuck in their private parts. Dust is a big issue with most litters, especially clay, causing severe respiratory infections. Some of the pelleted beddings like feline pine are ok so long as they don't have scents like cedar oil added.
Just because 1 person does not have any problems with it doesn't mean it's safe. They may have just gotten lucky. It has caused problems for lots of other people and their guinea pigs. For a long time cedar shavings were though to be safe until enough people reported problems with them that everyone started to listen. There are still a few people who don't listen and buy cedar despite all the scientific research and studies proving it's dangerous along with all the owners that have experienced problems or even lost their pets because of it. If it comes down to 1 person saying something is safe and possibly dozens of other people that have had sick animals I'm not going to risk it.
