It takes some practice but when you get them synced to dump a few seconds after the other and you get yourself in a rhythm your constantly pouring powder. My buddy even tried running four but it was too much.
I will never worry about spending too much on reloading gear again. Running 3 fx120's at the same time may be considered excessive. Not judging, just a wow moment for me.
I was tempted to buy an fx120 on a few occasions. However, after shooting numerous groups with an SD of 2-3-4 when using my RCBS Chargemaster, I just can't justify it. I'm sure it's nice to have the very best but "for me", I just don't see it improving my results very much.