I have a 650 (not for sale). How accurate the powder drops depend on the powder. Same as any powder measure. Ball powder, like H335, drops out of mine 95% of the time dead on. +/- 0.1 grains the other 5%. Stick powder, like Varget, is all over the place.
If I had it to do again, I would have got the 550. Much less expensive to do caliber conversions. I like the RCBS 2000 progressive also.