I've never used a Newberry Knife but I've seen them in catalogs.  Do they cut the bottom of the sack off, or does it do a vertical cut up and down the sack?  I've always believed the bottom of the sack should be cut off to allow for better drainage.

Right now I cut the bottom off with a scalpel, but I did manage to try castrating one finger of mine once in the process, so that's why I'm interested in the Newberry.  The cut on the finger took 3 stitches.