I like the 7 shot ones. An extra shot, why not?
I can gather a small handful of reasons that occur to
me, but I realize that there is room for both and absolutely a market for both, but I'm firmly in the camp that prefers the six shots rather than seven.
The cylinder, with the extra flute in it, looks "off" to my eye. And in the rimfires, where 10-shots are on board, that REALLY sets off a visual train-wreck, at least to me. However, plus-4 shots is quite an upgrade from 6 than a single extra shot. To me, I'm absolutely fine with 6. And aesthetics (admittedly!) have always meant a lot to me, and in some cases, maybe they mean a bit too much? I know what I like.
I also note for sure that I'm simply losing meat & metal in the cylinder for that extra shot that I didn't ask for, and the cylinder is pretty much -THE- place where all the pressure is contained. Obviously, S&W knows quite well what they are doing (with the exception of
Japle's gun...), they don't ship out "dangerous" guns, but in some ways, I am a simple guy and the six shots and meaty cylinder press my happy switch.
It does also complicate speed loader use if you've been running a 686 since the late 80s and you have a nice pile of speed loaders that now won't work with a 7-shot cylinder... but then again, that's genius marketing for any company in the business of selling accessories.
We've also discussed, in the past, if there is ANY different feel in the double action trigger stroke since your finger is now actually doing something slightly different... I would have to admit up front that if anything, it should theoretically improve the DA pull as your trigger stroke is now moving that cylinder slightly less distance. Now the first 686-plus (7-shot) that I ran had a VERY different DA trigger stroke than my 686-3, but I think I safely determined that something other than the shorter distance of cylinder turn was at work. But suffice to say, the much newer ILS gun with the newer-tech internals had a horrendous DA stroke in comparison to my favorite L-frame from the late 80s.
I do not know why the fixed sight L frame never seemed popular, perhaps since the L frame came in at the end of the reign of the revolver as a service weapon folks who were going to buy an L frame as an upgrade, simply wanted the more featured model? I don't know.
I can also say that on a .357 Magnum chambered revolver, at least being able to adjust the sights vertically is a
huge advantage for me, damn near a requirement. Even at a short 10-12 yards, I can see on paper a good 2 to 3-inch difference in POA between target .38 loads and full-steam .357 Magnum. Being able to easily regulate your revolver for the load you shoot most, even if you only adjust the sights once is a much-appreciated feature, IMO.
But yes, the relative rarity of the 581/681 does definitely make my eyes light up when I see them. I would not argue with your suggested "30 to 1" ratio, it mirrors my experience. Frankly, I almost never see them. And while on that subject, I find there are way,
WAY less 586's out there than 686's, too.