There seems to be quite a few from Zeiss, Leica, and CV.

How do they compare in terms of brightness, flare, distortion, and magnification? My feeling is that zeiss is the best in all regards, followed by leica, and then cv. Many people seem to state which viewfinder they prefer without going into the specifics in why.

More specifically,

1. I hear that the Leica's lock, is this true only for the plastic ones or do the older metal ones lock to? Locking would be handy but I'm not sure if it is a deal breaker or not.
2. Anyone feel the non-Leica ones are less accurate? The Leica ones I believe take into account the offset from the shoe to the lens. I'm hesitant to go non-leica for this reason. However, many prefer the Zeiss and this does not seem to bother them. I worry because I shoot at close distances (1-3 meters) often but prefer to not go with SLR's. I'm not that precise with my composition/framing.
3. Do they all have framelines, which allows me to see the most outside the frame. I really like framelines.