- "Screw in" is not a mounting method to guarantee exact positioning each time; the extremely fine pitch filter threads can not warrant it when the screwed-in surfaces come to contact with each other.
- Rubber hoods are prone to deterioration (mini-cracks, color-change, etc.) due to ozone and UV. Also they may lose their flexibility to retain the exact shape after some years.
Square hoods: Unless designed specifically for the angle of view of the lens they are to be mounted on, they may NOT function as expected by blocking the lower right corner of the finder on the RF cameras. So be careful. 46mm screw size is larger than the 39mm; consequently the square hood you are going to receive SHALL be substantially larger than the square Leica hoods and most certainly will block a great deal of the view in your finder.
OTOH, if you are going to use it on a camera having liveview then no issue at all.