Here's what I can tell you about the Westwater. I bought it for fishing in foul weather that I often see when fishing Great Lakes Steelhead. It's highly water resistant and has a good amount of space, but it is mostly a big pocket. Water resistance is probably it's most significant feature. On the inside, there is one zippered pocket and one mesh pouch. The outside has one smaller zippered pocket. It has plenty of room without being too big, you can fit jacket, multiple fly boxes & food with ease. Very comfortable to fish with.
There's a D ring on the pack so you could hang your net from that. It's great for my needs but I'd consider it a basic pack in terms of organization. It lacks a bottle holder as most waterproof packs seem to do but there's room on the inside for that. The build quality is what you'd expect from Fishpond. Overall I'm very happy with it.
You should have a look at the reviews for the Orvis Guide and Patagonia sling pack here:
Gear Reviews - The North American Fly Fishing Forum
They both seem to have very positive reviews and if you want a sling that has more organization you'd probably want to look at one of these over the Westwater.