I had a look through the new CV metal 21/25 finder last week end and it is great, very well made, solid and tiny. Distortion is well controlled and price is still reasonable compare to the Zeiss counterpart.
I would definitely go for the CV one if I had to buy one.
I did go for the new CV 21/25mm finder.
The Zeiss 21mm finder has a better eye point and higher magnification, but the new CV 21/25mm finder is still very good and a lot smaller.