Eric,
I really liked the orris sling and used it for years, the only thing I found wrong with it was not enough space when I started adding more and more fly boxes (Whole different problem...Lol)
For me I think the Fishpond sling is a really nice product and made very well, you can tell a lot of thought went in to it. But for me the design is backwards, where I am expecting to reach and grab stuff, they are on the opposite side. They do an integrated net holder with works very well on their lumbar pack, but on the sling, if you use it the net is in your face when you spin it around.
I like the ring on the orvis sling that for holding the net.