The least expensive super wide Leica lens (new) is the the 24/3.8 Elmar which retails for $2395. The Voigtlander retails for about $400. Zeiss finds middle ground for about $1,000.
The first decision I really had to make was, which focal length? Voigtlander, Zeiss and Leica also makes a 12mm, 15mm, and 25mm lenses. After doing some research, most users reported that the 15mm lens is more of a specialty lens. After buying and using the 21mm, I can't say I ever thought, "Oh, I wish my lens was wider." In Europe, it stayed on my camera almost all the time. Once in a while, I wondered if it was too wide as a general walkaround lens. Overall, it's a good comprimise.
While the maximum aperture is only f/4, the lens is quite small. It's hard not to bring the lens along.
Overall, it's a high quality lens and offers great value for the price. There is minimal vignetting at the corners and there is no noticeable distortion - straight lines appear to be straight. There is always some optical distortion with wide angle lenses.
