"A codicil can be quite a lousy idea" I don't see the logic in that. However, to each his own...
A codicil, because it isn't prepared by an attorney and witnessed, is considerably more vulnerable to a challenge than an actual will because it doesn't demonstrate the same forethought and followthrough.
For instance, it's a terrible idea to reallocate assets with a codicil, because the person who gets shorted will almost invariably claim coercion, sue over it, and have a far better chance of at least some success than would have been possible had the intent to make the same change been clearly expressed by a new will.
I've seen all too many instances in which attorneys fees ate up estates, leaving between little and nothing for the heirs.
