Over the past year I have purchased three of the grade necks you are asking about. I love the hen necks -- they are perfect for some of the small nymphs and wet flies I use. The Tyer's Grade necks are excellent IMHO. Granted, I am not a fantastic tyer, but I have tied some pretty cool parachutes in sizes 20 and 22. I have no idea how many flies each neck will tie ... same goes for the number of flies in a particular size. However, I've got a feeling these will last me for years.
Also, I purchased a silver half-saddle about a year ago. Sweet. It seems to me that maybe the silver saddle is a little more dense than the Tyer's Grade. The barbules seem to be a little closer together. Honestly though, there's not that much difference. I bought the saddle because I like pulling one feather out and tying 8-12 flies from one stem; saves me time from hunting 8-12 different feathers from the cape.

Just my thoughts.

Regards,
GQualls