I've been fishing a 580 for the last couple of seasons. I had it out in the backcountry yesterday, which was fun. So far I've landed some rather large browns and rainbows on it, plus a handful of Kahawai. I wouldn't say it has always been the absolute best tool for the jobs I've put it to, but it has often been the most fun. Just remember to extend your casting arc as the rod is bending much deeper than you will be used to. I think they're a fantastic tool for learning to improve your fly casting too, as you simply cannot rely on power.
The 686 is a fairly ballsy rod to be honest. It's a genuine 6 and a reasonable step up from the 580. This to me is the rod in the range that proves the 'fast-glass' mantra. I'll be getting one built soon, so will be able to give more detailed info at a later date.
Regards the ready to wrap, it's a good kit and has everything you need. I managed to build it, and I'm deeply impractical with anything like that. So if I can do it I think you'll be just fine.