No, it generally won't flare up. Also of course, the larger your reflector, the better your results will be. I used to have an old lantern reflector that was about 6 inches around. That one worked really well but I've had success with Maglights too.
I use parabolic mirrors all the time for fire starting. In fact, I keep one on the front porch to light my cigars on sunny days.
The trick with this technique, as usual, is to have REALLY good, dry tinder. Charcloth works well, so will 0000 steel wool and cat tail fluff.
There is of course another way to start a fire with a flashlight...
Needed:
1 small ball of 0000 steel wool, about the size of a golf ball.
1 Mini-Maglight with decent batteries (AAA or AA, doesn't matter)
2 Little bits of stiff wire small enough to stick into the electrode holes when you remove the bulb from the MiniMag.
To start the fire...
1. Lay your fire in preparation for a "One Match Start"
2. Remove head from MM
3. Remove lamp
4. Insert one wire into each electrode hole, being careful not to let them touch.
5. Touch the two wires to your 0000 steel wool.
6. When you see fire, gently blow to encourage the flame, place burning steel wool in laid fire.
7. Tend fire until it reaches desired size.
8. Re-assemble your flashlight, it should still work properly even if the batteries are fairly drained.
9. Cook dinner, make coffee, prop feet up, relax in the knowledge that YOU have made FIRE! (Just like Tom Hanks!)
10. As with all fires, be absolutely sure the fire is properly extinguished before you leave the area.
