I've bought both as gifts, and while I personally like the Dragonfly kit, the kids seem to dig the Delica a bit more. It's a bit sturdier too. As mentioned above, the danger with the Dragonfly is that inevitably someone wil try to close it like a slipjoint and break part of the lockbar or backlock 'mechanism'.
It pleased me to see, while I was over at my brother's place the other day, my nephews were trying to use this to 'cut' the tabs on some Lego boxes:
I guess when we were kids and would draw an archetypal 'knife' it would look something like a Mk. 2 'K-Bar' or a Lile 'Rambo' knife.
It always makes me smile to see that the typical knife drawn by young kids in our extended family always has a Spyderhole, and usually looks something like a Delica!