This has always bugged me as well. We’ve always been told that the odds to get an Epic or a Legendary are three times better with a Magic Key compared to what they are with an Iron Key. The problem is that, without knowing what the odds in question are, this is nearly meaningless. We don’t even have a ballpark, at least officially. There are plenty of threads with people giving us their own personal results on a small to less-small sample, but this isn’t reliable for the big picture.
By the way, it’s not mere speculation; I’m very sure the fact that a Magic Key has 3 times the odds of giving an Epic or a Legendary troop was noted somewhere official. I can’t remember whether it was in the game’s shop itself or on the website, and can’t seem to be able to find it now, but it was official.
In any case, from experience, the base chance to get an Epic or Legendary cannot be anywhere near 10% or above, it must be considerably lower than that (I think even the tripled odds have got to be lower than that, even). My own personal guess has always been that it’s maybe 1% or so for Iron Keys, and it gets bumped to 3% or so for Magic Keys. Maybe 2% raised to 6%. Maybe.
And the problem with this is pretty clear. Would you rather try your luck more often with a tiny, tiny chance, or less often with a slightly less tiny, tiny chance? Of course anyone would prefer the former to the latter, as they have a better shot in the long run this way.
Of course, it’s a bit tricky to compare how much Iron and Magic Keys are worth, since they’re acquired in different currencies, for the most part, and at different prices depending on what you rely on. Obviously, this doesn’t make much difference anyway, since you can potentially amass hundreds of iron keys without having to spend gems for them, whereas you’re almost guaranteed to have to shell out gems if you want to get any significant amount of magic keys.
Let’s just compare the prices for bundles with Gems, to at least get an idea.
The cheapest bundles:
15 gems for 1 magic key
15 gems for 1K gold = 1 iron key
Surprisingly, they’re at the exact same price, for these (and the next few bundles).
The biggest bundles:
450 gems for 40 magic keys, aka 11.25 gems apiece
240 gems for 30K gold = 30 iron keys, aka 8 gems apiece
Interestingly, even with the best deals for both, iron isn’t that much cheaper than magic. I’m surprised! ^^
This means that if someone spends gems for keys, magic ones are almost certainly a better deal.
Personally, I’ve always preferred spending gems on other stuff. Iron keys are enough for me.