Katalax does seem to have different ingredietns - it is a different consistency and colour for a start, but can't be bothered to walk downstairs for it!!
Gill - I wouldn't worry about them not liking food with Lactulose, Molly is such a fussy cat, and she is fine, she doesn't seem to notice - but she has it for constipation, not furballs, I dont know how well it would do for furballs.
I personally would only watch him for a few more days before going to the vet, just in case it is something more than moulting, and somethign that can be dealt with if it is picked up on sooner rather than later.