Never, never, never use a running ball for a guinea pig. Their spines can't handle the movement of the ball and serious injury and even death can result from it's use. If they catch a toe in an opening, they can lose the toe, limb or break bones. I volunteer with a guinea pig rescue and this item and those like it by other manufactures is the one toy we always warn new owners about.

Pros: use for hamsters

Cons: guinea pigs can break limbs or break their back in these

my hamster uses this ball and he loves running around the house in it. I have two dogs and i worry about them hurting the hamster, but with this ball i know that my hamster is safe from them. it's easy to get him in and out and locks securely. it's very cheap also.

Pros: Very protective, and safe

Cons: none

these are gresat because the critter can run around and get excersise and not get lost or stepped on

Pros: dont get steped on

Cons: na