That's the way a lot of people look at it too, and I'm sure that a certain percentage of times a lumnock would help. I prefer to keep my FOC higher to get a better arrow flight, I'd rather lose an arrow now and then to insure good flight insure a better placement.
I don't want to discourage you from buying them, it's your money, I've just learned too many lessons the hard way.
BTW my FOC is 21%.