I've been using the SL900 for about two years now. I bought 3 of these presses and sold two to friends who were also getting into some serious sporting clays shooting.
Of the three, I have had the least problems. One friend recently sold the SL900 and upgraded to the Spoler which is the cadilac of the shotshell presses. His main complaint was the priming system was not reliable and overall the press was undersized for the task. He often commented that Dillon should have based their shotshell press on the RL1050 platform. I agree but that would have placed them out of the market on being price competative.
Friend number 2 still has his but has managed to tinker with the priming system to make is more reliable. Two other people in the area have the SL900 and are using it w/o problems but the volume they have combined is 1/2 of any of us three.
My biggest complaint in the priming system will not consistently feed or drop a primer. The other troublesome point is the case feed will sometimes jam up with a hull not dropping freely into the tube.
The best approach to making the SL900 work is to keep it as clean as possible, clean the primer tray with alcohol and treat it with car wax periodically to let priimers slide freely and use TFE (dry plate lube) on all of the working parts to make the press operation as smooth as possible.
One of the most important things to keep in mind when using this press is don't rush or jam the op handle. The SL900 works best with smooth, steady and not too rushed strokes. All and all it's the best press out there for the money. I can load a flat of shells in under 30 minutes and that's not bad... Good luck with whatever direction you take.