I'm the odd man out here. I have a 550 with the case feeder. I like the 550 much more now that cases are loaded automatically.
Yes, I sometimes have a case that does not get pushed all the way in for primer seating-I have the .45 acp and the .45 Colt case feeder conversions- ( I deprime and resize off press, I prefer to do it that way). But its easy to feel when the case didn't get all the way in and a gentle push puts it in place.
Doing this allows me to concentrate on the seating stage, so I am always looking at the case with its powder charge.
As our friend Jack has stated before, anything that reduces hand movement is a good thing.
And anything that makes me concentrate on the seating stage is a good thing.
May the Force be with you.