I haven't been in N scale for about 10 years. Vision problems and minor nerve damage to hands from medical procedures. It can be no fun to get old. I usually purchased their assembled couplers. Cost more but I felt worth it. Less agrevation and parts loss.
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
I have assembled hundreds, if not thousands, of these things. All I can say is, yes, they can be a pain in the rear, but take your time and you'll get the hang of it. To me, the cost of the preassembled couplers is just not worth it.
Don't remember any flashing that you mentioned, except for where they are cut from the sprue. A knife or small file will take care of that.
Chuck - Modeling in HO scale and anything narrow gauge
Has anybody had luck with assembling the MTL coupler kits. I find this very difficult to work with such small parts that contain a lot of left over flashing. I am researching the assemble MTL couplers and possibly othe rbrands.
DMK