That is one use for them. VC Charlie used to start one with sun lite.
Built the same way except the holes were on the bottom and it was filed with gasoline. Wet a piece of paper or rag with gasoline and place over the fill slots. Position a piece of broken glass so the angle magnifies the sun at the point where the wet paper was. Position over a large hole lines with paper and fill with more gasoline and some rounds.
Perfect for removing small trees and lean-tos.