I've used my own boiled cider before, but not this. It's just a way of making concentrate by evaporating out the water. It raises the gravity of the cider but you need to use a lot more apples. 7:1 sounds like a pretty high concentrate though...mine probably came out to 2:1 at the most. You don't want to evaporate so much that you end up adding water back into it. Also people will tell you not to heat cider because of pectin haze and heat damaging delicate apple flavors. I did it and mine turned out fine.