Played From Either Hand

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K J 4 2
Q 10 8 7 5 4 3
8 6
6 5 K Q J 10 9 4 3 2
9 7 6 ------
K 9 A 6 2
Q J 9 5 4 3 10 7
A 8 7
A Q 10 8 5 3
J Contract: 6 hearts
A K 2 Opening lead: Q of clubs

This is another easy-to-make slam hand if declarers will just take a little care. But of 10 who bid the slam, it was an even-steven 5 each on the make vs. going down. The declarers who went down just weren't careful, especially since the hand can be made two different ways, making either of declarer's hands the master. Now, if you look at the South hand, the jack of diamonds is a loser which can't be helped, and you dismiss it from mind, except perhaps to lose it early, as some did, so as to have good communication. But you now have three low black cards which must be accounted for by a winner in dummy or you don't make. And that winner in dummy was, to some declarers, going to be trump by way of ruffs. So you can't lead three rounds of trump before getting around to those ruffs and you can't draw two rounds of trump because that still wouldn't leave you enough for three ruffs, and indeed, you'd better not take one round if you didn't get a diamond lead, because if you do and then decide you'd better lose a diamond for communication purposes, you may be met with another trump lead and now you can't ruff out all 3 black losers. (Actually on a spade lead, you'd have enough communication by way of clubs to get all 3 ruffs before touching diamonds. On a trump lead, indeed, you'd need to use those club re-entries: A of spades, ruff, back on a club lead, ruff a spade, back on a club lead, ruff a club. Conversely, on a club opening lead, you'd need to lose a diamond -- quickly -- since you wouldn't have enough club re-entires.) Capiche?
From that point, it's a piece of cake. Many ruffed an opening spade lead and immediately led a diamond, invariably won by East. Now (on, say, a club shift) declarers can ruff a spade, back with a club, ruff a spade, back on a diamond ruff, ruff a club high. If they took one round of trump, they would now ruff a diamond high (holding the top three trump with two out) and claim. If they haven't taken a round of trump, then can simply overtake the king of trump, missing only three.
But there is a twist here, making the hand somewhat easier, and that is a dummy reversal, which is to say you make dummy master, accounting for every card there. Forget about spades. The ace is indeed superfluous on this line. Forget about clubs (except maybe for entry purposes). They're solid. Trump are pretty solid, though don't get wasteful. You've only got one more in dummy than one of your opponents. You've got 8 diamonds. If there's a 3-2 split, you've only got to ruff out two diamonds and claim, thus (on say, a spade lead): Win with the Ace, lose a diamond, regain the lead, say on an unhelpful club shift, go to dummy on a trump lead, ruff a diamond, back on a trump lead, ruff a diamond high -- that clears the suit -- cash a high trump, and now you can ruff a spade for a re-entry to dummy and claim.
Several declarers had the diamond suit handed to them and didn't notice. In one case it was just about literally handed to declarer. East goes up on a low diamond from dummy and leads a diamond! Ruffed! King falling! Not noticed. Others did their own diamond lead from dummy on the second round, necessarily picking up the king. Not noticed. Those who didn't notice, incidentally, didn't necessarily go down. They simply got their three ruffs in dummy.
The declarer who took three quick rounds of trump didn't make it. He now had neither enough ruffs in dummy for playing from the closed hand, nor enough entries for playing from the open through ruffing out diamonds. One declarer got overruffed on the second round of diamonds. How so? Well, he failed to notice that in taking the opening spade lead with the ace and then ruffing two spades, West pitched a diamond on the third round! Careless.
I went through the best possible defense and found the dummy reversal still feasible. Heart opening lead won in the closed hand because declarer can lead diamonds from here. Jack of diamonds taken by the king and hearts continued. Okay, no problem. Won in dummy and a diamond is ruffed. Go to dummy for the last round of trump and ruff another diamond. Now you'll have an entry back to the diamonds on the third round of clubs.
A simple hand played from either hand if declarer will just count his winners, or watch his losers and take care of them, give some thought to establishing that 7-card suit in dummy, or make sure you ruff three times in dummy, and don't cash the ace of spades until later. I would say, don't cash any established winners here until later, except for communication purposes.