Re: want opinions on fly fihing vests....
I have the Fishpond Marabou Vest which is similar to the Flint Hills Vest. It's only my second vest but I'lll use it forever. It holds everything I need, is very light, not bulky, and pockets are easily accessed. It's also very rugged. I've used it for a couple years and scaled banks, busted brush, fell on rocks, hot and cold climes and it still looks new.
Things I don't like. The slim-flat design doesn't allow you to hold many fly boxes up front. I'm limited to two C&F medium boxes which is enough for me. If you like to carry multiple boxes you'll have to stuff some in the back or make room up front. It all depends on how you organize it, I guess. I'm a stuffer.
Right now mine holds everything I need to use my 4, 5 and 6 weight rods and go after trout and bass. I also really like the hand warmer pockets. I also have enough room in the back for a warming layer, gloves and a beanie.
If you're a big guy and want to carry more stuff up front, I would consider going with the Gore Range Tech Vest due to its protruding pouches/pockets.