I have a cat and never used a cat net. The cat never went near the babies in their cots or even now in their beds. I thought the image of a cat all tangled in a cat net going bezerk over a baby's head was worse than the thought of a cat sitting in the cot.
The cat never went near the babies in their beds, but I did try one on the moses basket to stop them from sleeping in there when the bed was empty. The cat just used its weight to push it down and nested on it - useless!
It just sort of sank in the middle into the bed with the cats weight (she looked very comfy) - I can't see the point in the nets really. I would have been better off covering the moses basket in tin foil