The odds for playing the spade suit for four tricks is about 74% and the odds of the diamonds playing for 5 tricks is about 68%, so the slam is about 50%. Perhaps not as good as it first looks.
In terms of the bidding North's 4
♣ rebid looks a little strange. I'd have thought either a simple 3
♦ bid (which must be forcing) or a jump to 4
♦ if this shows a 2-suiter would be more normal. I guess North was just cuebidding his lowest control but thin slams, which this one would be with South as a passed hand, are more dependent on shape than controls, so showing 5-5 is better. North still has the strength to bid 5
♣ over the 4
♥ cuebid and will be able to leave the final decision to South.
As South has an opening bid in North's eyes, I would expect South to bid the slam given North's strong bidding and excellent diamond holding. However, as the odds show, all decisions are correct
p