Depends on whether you prefer or dislike the shorter focus throw of the later models.
My girlfriend uses the K version and I can only say that it is a very nice lens to use, wide open or stopped down.
It is very different, optically, from modern lenses, but that does not mean it's a bad lens. It is, in my opinion, a good and perfectly sharp lens, even when used wide open.
Below is an example of a photo I made using a Nikon D800
DSC_1603-Edit by
b j, on Flickr
If you are looking for a manual focus 50 f1,4, and find agood deal on this one, and the longer focus throw does not put you off, I can hoghly recommend buying it