I used the Fresnel for three reasons.
1) I had used a normal lens and it cause a fair bit of a "fish-eye" effect
2) I had some fresnel material to try out
3) being a flat sheet was a lot easier to cut to the required size and mount in a little box.
It does reflect light from the room but not too badly, being flat it would be easy to add a layer of non-reflective film to when I get some. I'm currently restoring a Pye V4 television and this has a purple plexiglass implosion screen - it looks strange when the set is switched off but when playing it reduces glare and gives a very good picture.
The stuff for cars might be a bit coarse the reading lenses would probably be better...I'll keep an eye out for some. I too have a credit card one somewhere that came with the magazine Elektor - it's very useful for reading small component numbers!
Fresnels are used for rear-view magnifiers because a normal lens 50cm diameter would be difficult to stick to the back window and very very heavy!
Another idea you could try is to make your own lens like the old TV magnifiers -
http://www.tvhistory.tv/TV-Lens.htm fill something see thru and the right shape with ground nut oil?
Dom