I like these boots a lot -- I've fished in them for some 10-12 days now, and here are my initial impressions:
BOA: I really like this system -- it makes it very easy to put the boots on and to take them off. I am looking forward to using them in the winter, hoping that it won't ice up like my regular laces do. I am not able to get the boots as tight as I did with laces -- I get to a point where it's pretty hard to spin the wheel, and I'm afraid of breaking it.
Fit: I wear 10-10.5 street size, and the size 10 Korkers were the ones that fit. I tried 11's and 12's, thinking that with the waders I need to go up a size. I almost made the 11's work with an extra insole, but the BOA didn't let me crank it tight enough. Go with your street size.
Kling-on rubber: very poor. I tried it out on the Eagle River (CO), and feel twice in the first hour. The rubber soles don't stick to anything. But I'm guessing they'll work well for hiking and for sandy creeks in WI.
Felt sole: pretty good. It still slides around mossy rocks, but works much better than the rubber.
Studded felt sole: best choice. I used this on the Green River (UT), Arkansas (CO), Yampa (CO), and it worked great everywhere.
The outer sole is glued to an orange plastic, and that plastic seems poor quality. One of my rubber soles cracked while being removed (Backcountry.com already replaced it), but I see hairline cracks in the other soles, just from regular use.
Since soles are so easy to swap, I'm using the rubber sole to hike/motorcycle to the river, and then swapping to studded felt for actual fishing.
On the overall I'm very pleased with the boots, now that I found the size that fits me. The sole interchange system is good, and I look forward to trying out the Svelte sole when it comes out too.