Although problems are the exception, not the rule, if the set is for anyone else but you, I suggest you open and test the important pieces prior to the big day. Last thing you want is to discover a bad car, PSU, lane changer, or lord forbid, the APB. If you find a bad part, there's still time to get a warranty replacement from Hornby, maybe, but at the very least you can mitigate any disappointment by steering around any problems.