We sell more SKMR3's over the SKMR since a Christmas Tree type tends to be more popular, and its' not so busy that it's in the way like some other Tree type. The SKMR is still very popular for people who do not prefer a tree, we'd be happy to help you decide as we have both options in stock for a K624i
What type of shooting are you looking for this reticle to accommodate? If you prefer a less cluttered view and plan to dial elevation for every shot then the SKMR will serve you just fine; however, if you ever think you might use the reticle for holdover then the SKMR3 will definitely help.
Of all the unsolicited orders we recieve, the SKMR3 is by far the front runner. Even when customers call and we have the chance to present the differences the SKMR3 is still the leader.
Having marks to hold off of vs having to hold in space I find is easier. Once you get behind the reticle and spend time with it, it doesn't seem "cluttered" IMHO. I used to be anti tree style reticle and a big fan of the H2CMR style. After shooting with it and spending time with them I much rather a tree style reticle.
That being said I do really like the SKMR layout with the .2 mil spacing for wind holds/movers if you are looking for a less intelligent reticle.
Trees are great when you have time pressure - you have the option to not twist any turrets. At long range with mild recoil cartridges like 6.5CM, you can get back on target after a shot and use the tree to measure your miss splash. If you shoot extreme long range and dial up all of your elevation, you may need to hold some remainder of elevation in your reticle - and a tree lets you still hold for wind. But some folks find them cluttered. YMMV, lots of reasonable people have different reticle preferences.
You can hold for wind and elevation with the SKMR3, which you can't with the SKMR. If you're going to dial your wind and elevation, then maybe the SKMR is a better choice. I use mine (K624i SKMR3) for PRS shooting.