Tried them; they cook slow. Packing the sheet of glass and black pot made them not practical for me.
... also tried reflector ovens for the campfire and they work too; but can be hard to keep things from getting overcooked in places.
For small oven cooking the Coleman oven for the 2 burner propane stove worked better than most things (but was enough trouble that I don't bring it; or the dutch oven anymore)...
Since I just cook for me now I keep it Very simple...
Enjoy!