Electronic powder dispensers are very accurate and easily programmed for a given weight. However, it takes up to 30 seconds to deliver each load. That's appropriate for maximum loads, sniper teams and bench rest competition, but not for pistol shooting in general.

A powder hopper can be very consistent, say +/- 0.1 grain, depending on the powder and technique*. It is surprisingly easy to establish a load, especially if you have an electronic balance. I have mine on a stand, mounted on a 12"x15" board. I can drop 200+ loads an hour, and it can be mounted on a progressive press.

* Proper technique includes keeping the hopper half full or more, rapping the handle twice top and bottom to settle the load, and tapping lightly on the side of the hopper every 20 drops or so. Only adjust the cylinder when it's facing the hopper and check the weight every 10 drops. Take care dropping into a powder pan - you can bounce 0.1 grains right out of it if you're not careful. I bring the pan up to touch the drop tube.