I hope this does not come to late ( I have just come back from holiday ).
The 45mm is my favourite lense, it is always mounted to my fm3a. When I bought my fm3a they did not have it in stock so I purchased the 50mm f/1.4 afd (which I now regret). I picked the lense a month later on after much deliberation.
This is a fantastic lense, the build quality is great and the results are excellent. I shoot hp5+ developed in acutol and printed in my darkroom and the results are first class. The fm3a and 45mm lense is a great combination, I try to carry it everywhere I go because it is small and light. A welcome relief after lugging my rz around all day.
There are very varied reviews, the main issue seems to be the price. I think the build quality alone justifies the price nevermind the results.
Ken Rockwell gave his opinion without ever using the lense. Here are some *real* reviews.