I tried them years a go. It works ok, but I prefer to use a set up like we use in fire starting competition at Friendship If you know how to find tinder there is no limit to how many fires you can start and the whole thing flint steel charred cloth and bag will set in the palm of your hand and only weights a couple ounces.
The other one I carry on a long hunt like in Canada is a magnesium block with a striker built in its something you have to learn to use but it works even when you have to start a fire with every thing wet.