JJ. I tried the concave make-up mirror about 20 years ago.
Wow it was bad
Terrible scattered light due to being 2nd surface coated (aluminised on the back instead of the front), distorted image due to mirror not being perfectly concave, and would be worse over distance due to being spheroid instead of Parabolic.
But it cooled quick
Colin, I also tried the 'Magnifying Glass' scope build too.
Apart from the poor quality of the optic itself it was a very nice richfield f4