Well, actually there a little bit more versions. But usually you can find two - Mir-20 20/3.5 and Mir-47 20/2.5.
They look almost identically. Main disadvantage is large front lens and inability to mount front filter (but there is mount for rear filter as well as 3 provided filters - orange, yellow-green and UV). I think Mir-47 (it is also produced in K-mount version) has better perfomance and bokeh.
My mir-20 is in poor condition. M-A Switch for diaphraghm control is broken and I think lens was dropped on floor. Still it produces nice results on film and on digital. And I bought it for 4x Guiness beer 0.5L
P.S. Photos are taken with Zenit 122 soviet camera, Kodak T-MAX 100 film, processed in my bathroom with Kodak D-76 developer.