Cap Feeder Singulation specification should start with the real closure.
Singulation prevents double feeding, overlapping and irregular cap spacing. It is especially important where the capper has a fixed cycle or where a pick head, starwheel or chuck must receive exactly one cap.
For a better buying decision, the useful comparison is not only hopper size or headline speed. It is how the feeder behaves with your closure, how the capper receives the cap and how easy the line is to run after changeover.
The safest specification route is to start with real closures, target output, line photos and the exact point where the cap must be presented. That avoids choosing a feeder on a generic speed figure that does not match the cap or capper.