>>Having the correct hex key is the secret.<<
Mind, I have every damn conceivable size from 1mm to 8mm, in 0.5mm increments, and all US-Standard sizes from 1/8" to 5/8", including some of the real oddball ones in between.
And in use, over the course of the years....I can find one to fit less than half the time...between strippage prior to me getting to it, corrosion, and just poor machining, rarely do any of the 'proper' ones fit.
That's why I think the things are a completely hideous idea, besides the fact that you can't get leverage on a hexkey like you can a wrench.
It just doesn't make any sense at all to use this kind of fastener, with all the hassle, I can see no valid reason for it.
I wish the egghead engineers who design crap like this were forced to own the product....things would get simpler in a hurry.