I have a casefeeder on my 550.
I can really only say good things about mine. I load .45 mostly, but also 10mm, 38/357 and some .40.
Supposedly, I was supposed to buy more parts for the casefeeder to work for the other calibers (other than .45). It works great without the extra parts.
Honestly, mine works *nearly* flawlessly. The "problems" I have had are:
1. Occasionally, the hopper jams
2. Sometimes the mechanism that pushes a case into the shellplate doesn't quite get it in far enough
3. The camplate for the roller follower took some time to get aligned JUST right.
When I say the hopper jams, I mean that a case doesn't drop into the tube, and instead, gets pinched between the wall of the hopper and the wheel. Again, I have the wheel/conversion parts for .45, and use it for all of the above listed calibers. Guessing here - but I would say a .45 case jams the hopper once ever 1000 rounds. More for the other calibers - probably more like once every 300 or 400 rounds. When you notice it (either you haven't heard any cases drop into the tube for a while, or you run out of cases at the shellplate), you look up, see the jammed case and unpinch it. This takes less than 5 seconds.
The feeder that pushes a case into the shellplate, probably once every 200 or 300 rounds, doesn't quite put it in far enough, so that the machine jams, when the case doesn't go into the size die. 9 times out of 10, relieving pressure on the lever and trying again fixes this.
Still other times, the case won't be seated deep enough into the shell plate for the primer to line up. Again, a wiggle of the lever usually fixes this. I'm not sure if this is a function of the case feeder, or the Dillon press in general.
I bought my machine assembled, and made thousands of rounds with it before I got enough of a "feel" to realize something wasn't quite right. I ended up needing to adjust the camplate for the casefeeder roller follower. The cam was too far away from the follower, resulting in too much bending stress on the shoulder bolt the roller follower runs about. Adjusting the cam plate to be closer resulting in interference between the index star (on the shellplate) and the camplate, so I had to file/grind a small amount on the camplate - but the machine runs much more smoothly now.
Overall, I think I'd give the 550 casefeeder a 93% grade.
I have never taken the feeder off to convert my press for loading rifle, but I understand it's a bit of a project to take it off and reinstall.
I have no idea what the actual loading rate is with/without the feeder, but I find my "technique" to be very natural and quick.
I always keep my right hand on the lever. While my right hand is pushing down on the lever, my left hand is grabbing a bullet from the tray. As soon as I prime the case, I index the shellplate with my left thumb (bullet still held between thumb and forefinger), and then I place the bullet into the mouth of the case in station 3.
I have a hard time believing a bullet feeder OR auto-indexing would speed me up much. As it is, I can make a boatload of ammo right quick........