I agree,
@chuckroast. I have most of the original LTM Color Skopars - the 21, 28, and 35mm versions; I'm just missing the 50 (I have more than enough 50mm lenses as it is!), and they're all pretty incredible. Personally, I just stick with the regular circular "hood"; not only does that keep each lens nice and compact, but it means you can just slip the lens cap over the front. I don't think I've ever really had a problem with flare on any of them, either. Looking through my Lightroom library I can only find one image from the 21mm with any sort of flare at all, and for a lens that wide and a hood that small, I think that's pretty good going.
Sadly, my 21mm has some of the dreaded "haze" inbetween two of the elements. The only time I ever really notice it is when there's a strong light source in an otherwise dark shot, but it's rarely that objectionable:
View attachment 4882015
Incredible little lens. My Leica Ic usually has either the 21mm or 28mm Color Skopar on the front, but the 21mm in particular makes it a very easy walk-around camera.