Laowa 15mm f2 or F5 for shooting square format as the digital SWC

[Einst_Stein]

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Anyone has direct experience with both version of the Laowa 15mm (M mount)?

Is anything else besides the price, size, lens speed (hence large aperture gradual focusing effect)? Say, corner performance? distortion?  

I am particularly interests in their performance if shooting M in square format, and wonder if the f5 has any other advantages.

Edited March 6 by Einst_Stein

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[henning]

The f/2 lens is better optically, even in the centre. However, the greatest difference is in the midfield and corners, so you might not notice it as much. Also, the f/5 has quite noticeable complex distortion, while the f/2 has so little I found not need to correct it in nearly all cases.

The real difference in use is the larger size of the f/2. The f/5 is tiny, whereas the f/2 is generally the size and weight of the 90 f/2 APO or pre-asph, although slightly shorter. Travelling, I would prefer and take the f/5, if I still had it. I kept the f/2 for its performance. Both of these are definitely upgrades over my previous 15, the Hologon, which I bought new in 1974 and still have.

There are good reviews at: https://phillipreeve.net/blog/lenses/leica-lenses/ which highlight some of the differences.