I have the St Marie diopter setup on one K31, and a scout scope on another.
The diopter set is a quality piece. Sturdy and reliable, with repeatable 1/4 moa clicks. I've used it in silhouette matches, and in HP prone matches out to 800 yards. I very happy with it. The only problem with the dipoter set is the rear sight, depending on the load, may or may not have enough elevation to get you to 800 yards. If you are thinking of getting the diopter set, wait a month or so. St Marie is coming out with a new front iris assembly that is a bit lower. That will allow the rear sight to be zeroed at a lower setting and so have enough elevation adjustment to be able to shoot out to
1000 yards.
For the most flexibility, get the St Marie clamp on scope mount. A few shooters at my silhouette matches have them and have been happy with the performance. St Marie makes 2 rear diopters. One that clamps onto the rifle, and one that clamps onto the clamp on scope mount. They are otherwise identical. The one that mounts to the scope mount allows you to adjust the diopter fore/aft for eye relief. So you could get the clamp on scope mount, and then if you wanted get the diopter set later and use it with the scope mount.
On my scout scoped rifle I use Darrell's scout mount. He doesn't have a website, you contact him directly
[email protected]I have a rifle with an S&K scout mount and I think Darrell's is a better piece of equipment. Though it may look in pictures like the Darrell's mount puts the scope too high, in reality it is no higher than an S&K or the one AIM sells. It offers more flexibility because it has more cross slots. I have 2 of his mounts with well over 500 rounds through the rifles since zeroing and niether has moved.
I have 2 Leupold M8 IER scout scopes and really like them. I've tried the NC Star scopes. They work, but are not in the same league. The Leupold can be had for around $200 new if you have a C&R license. I also recently aquired a Burris 2-3/4X pistol scope, used, at a gun show for just over $100. It compares quite well with the Leupold.
Here's a pic of my K31 scout scope rifle