I have a 6" that had fixed sights, but I got adj. rear sights for it. If I had it to do over again, I wouldn't have wasted the time and effort the adjustable rear sights. The fixed were fine, and I've never had to touch the adjustable ones.
I think I remember seeing a 4" 2206, but I'm really not sure. I tried looking up it up on the web when I first saw this post, and I was amazed at the negative comments I found about it. Maybe I just got lucky, but my 2206 has been a fantastic gun. The only ammo it won't shoot is the cheap Remmington Golden Bullet. Everything else cycles just fine. And I really love the magazine release.
I read the Gun Tests report and had to wonder what they were smokin' when they wrote that one. Their experience with the 2206 and mine were nothing alike. Of course, they probably just shot it once, and I've had mine for years.
I don't know why they didn't catch on, unless having the lug on top was just too radical for most folks. I hope someone else will know if there was a shorter barrel for the 2206 (maybe that was what the 6 stood for?), but it's been so long, I may just be thinking of the alloy model.