In terms of "red edge" my 21 Skopar (LTM version) has improved significantly with the new firmware, to the point where I find it unnecessary to use Cornerfix 99% of the time. If I had a shot with clean white at the edges, it might need Cornerfix. But by the same token, so would my pre-ASPH 21 Elmarit. (And, BTW, I can now say the same about the 15mm when coded as a 21 pre-ASPH).
But beware, because there seems to be a fair amount of sample variation in the Voitlander 21. A friend got one back when I did (when they first came out) and his vignetted in the corners several times more than mine. Then again there seems to be sample variation in Leica lenses also, witness LCT's comment above that his experience with the Leica 21 pre-ASPH is quite different from mine in terms of flare. Again with that lens, I have a friend who likewise found it has virtually equal performance to the ASPH, and yet another friend who found it much less sharp wide open--although not flaring any more than the ASPH. We'd like to believe at the prices Leica charges there aren't sample variation, but the evidence doesn't always corroborate that. In fairness, if we're talking about lenses we got on the used market, we can't really be certain what's gone on inside them before we purchased, even if the outside looks pristine. It's very difficult to see anything inside a 21mm even with a flashlight, due to the optics.
