Well, its not a chest pack, but I use a Richardson chest box. Downs makes a similar product, cheaper materials but a lot easier on the pocketbook.
Richardson: http://www.chestflybox.com/
Downs: http://www.chestflybox.net/
I love the similar internet addresses, lol.
Seriously, changing from a vest to this thing was a huge upgrade. You don't put fly boxes in them, it is a wearable fly box. Getting flies out is much, much easier, I went from struggling to find the right system to the perfect system. I paid for it, but it'll last a lifetime, I'll likely never buy a regular fly box again.
There are endless accessories. A leader wallet and floatant holder were musts for me. I hang nippers, thermometer, etc. off the straps on zip lines, and just use a safety pin to attach my license to the back. You can affix magnifying glass and lights if you choose, I do not.
As for the fly holders, you can customize as you choose. Compartments, strip foam, pads, etc. Do one tray one way, the lid another, and the next tray another if you want. I replaced all of my original foam with C&F inserts, and even spaced them as I like to have a streamer area, a midge area, etc.
The shortcomings for me are places to put tippet, shot, car keys, and camera. The camera was especially tricky, I had it velcroed to the front when I took it, but that was too big and it came off, ultimately losing me the camera. My next camera will have to have a better system, maybe a belt pouch or something. I'm sure with the right accessories I could have avoided those hassles. But I just use pants pockets, or on longer trips where I want food/drink, a belt pack.