I dont have experience with either of those grinders but Id suspect neither of them would grind sufficiently fine enough for espresso. It is generally accepted that the EM0450 is the minimum required, it has the same guts at the EM0480 but with a more plasticky exterior.
Is there any reason why you cant just use the same grinder for decaf? Its pretty easy to empty to the EM0480 hopper and you shouldnt really be storing your beans in the hopper anyway.
Itís certainly nice have a separate grinder for decaf, I have one myself. Decaf generally requires quite a fine grind so buying an inferior grinder is a waste of time & money IMO.