I'll add my .02
I have used the AGC and Marsupial (current) harnesses. I've like them both and have really never looked at the FHF stuff.
I saw the this new FHF harness and liked a lot of what it had to offer, so I spent the big price and ordered one. I got it this week.
First impressions were that it was a very well built set up. I ordered the bino pouch, rangefinder pouch, extra pocket and the wings. I put it all together and was overall impressed. The wings definitely make the accessories feel more stable. The overall quality is there.
What I didn't like was the length of the straps coming off the back of the harness. They are just too long and even when using the elastic keeper I couldn't get them to lay flat. They would bunch up or come out of the keeper and it was just to "strappy". The Marsupial has the same set up but the straps are shorter and work much better. I also had a concern about the raised edges around the harness itself. I could feel them a bit under the shoulder straps of my pack and it was a bit annoying.
I was overall pretty pleased and the harness felt comfortable until I put my pack on. With the side wings and accessories on, it just didn't work with the straps of the pack. I tried all kinds of adjustment moving the harness up and down (I prefer a high riding harness) and I tried to adjust the straps on my pack a bit as well, but I couldn't get comfortable. The straps on my pack were landing on the buckles of the harness. In the end, I really wanted to like the harness, but because I couldn't get comfortable with a pack on coupled with the extra long straps on the back, I made the decision to send it back.
Build quality is great. It was comfortable when not wearing a pack and there are a lot of great features, but in the end I still prefer the Marsupial.
I'm sure this is going to work for a lot of people, heck, I wanted it to work for me. Just offering a different perspective.