Pros and Cons, I'll make this short and sweet:
--PRO--
Fantastic L-frame hunk of tool, will last forever with proper care. Enough heft and girth to make shooting full nuts .357 Magnum enjoyable. Accurate, extremely well built and fantastic DA trigger that is warm to tuning for an even BETTER DA trigger, and obviously... an exquisite SA trigger. Scarce in production compared to the 586, and extremely scarce in production when compared to the 686.
--CON--
It's all about the price. The 581 is exactly the same as a 586 except that it has a fixed rear sight. The 586 is exactly the same as the 686 except it's blued carbon steel rather than stainless steel. Unless you really, really prefer the look of a fixed sight S&W revolver, there is nothing about a 581 that is an upgrade over the 586, except scarcity... if you like scarcity. If they had made the same volume of fixed vs adjustable sight, these would go for less money. The adjustable sight on any/every S&W revolver is NOT cheap or fragile, the fixed sight guns are lovable but there is very little reason to choose one over an adjustable sight, especially in a K, L or N-frame gun that won't be carried in a pocket.
SUMMARY
It's all about price. Folks typically chase a 581/681 simply to add a scarce, rare-ish revolver to their herd. It is not an upgrade over a 586/686. Unless you very specifically desire the smooth look of a fixed sight revolver, it is a downgrade. But they are desirable specifically because there are far, far less of them.
If it is priced like a 586, it is a very good buy. If it is priced LESS, it is a steal. If it is priced higher, it is a "collectible."
