Ive found a well polished and waxed rotary drop is incredibly accurate.
I purchased an FX120i awhile back and naturally I had to test all my other scales against it.
I wont get into how all over the place my CM1500 was. However, I did test it against my 505, which the 505 was dead on as I figured.
I also tested it with 8208 which is a finer short cut extruded from my Hornady rotary group. I needed 27gr for a break in load for my 6AR. So I set up 25 cases, started adjusting my measure until I was hitting 27.02 consistently. For grins I did a 5 drop test and ended up at 135.16. I did another 5 drop and ended up at 135.12. Ive had similar results with ball powders like AA2230, H335, CFE 223, W296. Ive never been more than a few 100ths off on a 5 drop test with ball or a short cut finer extruded powder. When you get into the 100ths off in a 5 drop test, you know youre on the money, and that value is statistically unimportant at that point.
Moral of the story? Buy a decent rotary drop, Redding, Hornady, RCBS, whatever. Strip the paint out of it. Polish it to a mirror. Wax it. Run graphite thru it to lube it. Store it with used drier sheets in it to keep static away. And you wont go back.