I'm still trying to figure out why the handheld parabolic dish would be any better than a simple magnifying glass - if your goal is to start a fire using the sun. Maybe the dish would work a little better on partly-cloudy days.

A few years ago I spoke to a Coast Guard helicopter pilot about emergency signals. I asked him what was the best (simple) emergency signal that a person in a kayak could use. The intention was to identify a simple, effective signalling system - if a paddler needed help a long way from shore. His reply was that signalling mirrors are still one of the best tools available. Those simple signal mirrors - that you often find in survival stores - can send a bright flash over 20 miles. Provided it's a sunny day, the helo pilots are more likely to notice that bright flash of reflected sunlight ... than anything else.

Signal mirrors are compact, inexpensive, and lightweight.

[Obviously you need something different for cloudy days, or emergencies at night].

Pete