I had one 'glued' on my Leica MDa long time ago.
Good lens and very affordable, compared to the Tri-Elmar 16-18-21mm which is the closest to 15mm from Leitz.
No descent way to put filters on it (gaffer tape is your friend).
The plastic optical viewfinder is not that mechanically resistent, just be careful...
If you like that focal, then is certainly worth the money!
I also was an early purchaser. I never even thought about replacing the plastic finder with a metal finder. However, if a metal finder were significantly smaller than the plastic ( and cheap) I would consider switching.
The finder that came with lens is very bright and clear.
I usually mount on a screw mount Leica for a very compact kit. However, for me, this is a difficult lens to tame, and not an everyday shooter.
Indeed. I recently bought my 15mm v1 used at a very good price, sold the plastic finder and replaced it with the more recent metal one. The view through it especially due to having actual frame lines is so much better. Now I can actually compose my photos and level them correctly before I take the pic!
Plus the build quality is obviously so much better. All the CV metal finders I have are excellent.