I hereby disclaim that I have no experience with hoppers at all.
If you're open to other, non-hopper solutions to holding disks, though, you may want to look at teams like us or 973, who stored disks in a line, not stacked on top of each other.
I can testify that our robot's tray of disks worked well. There was only one match where we had trouble, and that was due to a piece of the orange polyurethane belt's black electrical tape being ripped after two regionals and half a championship, with no maintenance. 973 was at Archimedes (we allied with them for eliminations) and both won LAR and were finalists at SVR.
You can see our robot's videos on
our Youtube channel, if you're interested; I don't know of any of 973's videos.