I am a big fan of these cubes. They are a good value when cheap at home depot.
I use them all kinds of different ways, but probably the most common is to relight a pile of spent charcoal right on the grate. I put ONE cube in an indentation of used charcoal, light it, and come back 10 minutes later to add new coal and go from there. As long as you have enough coal and cather it umder and around the cube, it will light right up.
The work great in a chimney of course, and i know others who use them to even start a minion style burn in the smoker.
Net: i light charcoal using all kinds of methods, and these cubes are just another (good) way of doing it!