I have not used the Shelborne head, so about all I can tell you is that we compared both when we bought our Massey and we could not see anything worth the extra money for the Shelborne.  We are happy with the Massey.  I can't comment on parts cost, because we have not bought any parts (other than for a gear box seal).  Our first Massey head was getting close to needing new fingers when it had an unfortunate meeting with a tree while it was on a header trailer.  Our current head has 3 seasons on it and it is still in very good condition.

The pictures are from 2005.  One variety had a lot of smut that year.

There is a movie of the machine running HERE.  You will need Quicktime on your computer to view it and it is 6 mb in size.  It will take a while to download on a dialup connection.