The Allen wrench holder is a minimalistic approach. It will keep your flint on the key ring but it will not provide much of a handle. I put it on the tip of my left index finger and scratch with my pocket knife or the utili key (which happens to be on the same key ring). That works pretty well and the sparks don´t hurt the finger. It just takes a little practice. Just don´t cut yourself.
Some of the pistol ones use regular lighter flints. They produce slightly more sparks than a lighter but they are easy to use with one hand and easy to aim even without practice. They are too bulky for EDC but I think they are OK for a BOB.