I use one for .223, 7x57 and 308 with no issues. The handle does require an amount of pressure and you can actually view the shell holder assy moving clear of the backplate, if you can't see this happening, something is jammed, maybe the pin/plunger that passes through the body and pressed by the lever. The jaws of the universal holder that hold the case rim are very easy to move from side to side when a case isn't installed, once again something is jammed if not.
As for not centralising, the holder does have a degree of self catering when it's free floating, however when a case is in place within the jaws it can bind slightly against the backplate and sit off centre. To solve this momentarily add a small amount of pressure to the lever as the pilot enteres the case neck to slightly relieve pressure on the case and it will centre. You'll soon get the hang of it after a dozen or so, few hundred you'll be pro!!
The three way cutters are excellent once set up, but they can be a faff (nearly launched into the scrap bin) until you have a good look at how they work. You can go from putting a razors edge on the case to none or very uneven cutting litterally in the turn of a hex key. Once set up though it's an excellent finish.
Good luck.