Looks like the difference is $15.
I bought one from them, but I can't remember which brand, I think it was the general one. IT worked OK. I stopped using it and went back to the hard short one that came with the lens. I carry mine in my pocket, and the rubbery collapsible one hung up too much.
They are designed to 50mm, but I never saw any vingenting.
Zorki 6 with 50/3.5 Industar
Leitz Minolta CL with 40/2 M-Rokkor
Digital and Film SLRs
Every real Black&White picture has silver lining.
It's not the size of the camera, it's the emotion in the emulsion.
Reality is just a shadow of four-dimensional space-time.