I would try to explain the possible negative effects of doing this. It’s not the 90s, when these curser effects were “hot”.
As a customer, I’d be be happy to be told it’s not a good idea if there was a reasonable explanation.
If the website is a hobby site that the customer will use for himself, friends and family only, it might be a nice “feature”, but if it’s a business website aiming to turn visitors into buyers, my advice would be to try to talk the client out of it.
Of course, you could just do what the client wants. It’s their money after all.