I have a 750 upgraded from the 550 - I am happy with the upgrade. I have loaded 2000 rounds of 9mm And 2300 rounds of 45 ACP using SNS coated bullets.
Yes as with any press I had to learn how it functioned and make a few adjustments.
Primer system works well, yes it stays much cleaner which helps.
The primer bars lg and sm are different in that there is a channel in the bottom - not solid with the diagonal slots.
the one thing I found is that while Dillon sells a 550/750 Allen tool set - I need the tool set for the 650 for the primer slider bar adjustment screw and casefeed arm adjustment screw use the 5/64 Allen head wrench.
So overall I am happy with the performance and build.
Jim