First off, let me say these little plastic cones are a game-changer for feeding live bloodworms to my finicky eaters. The suction cups held surprisingly well during the first few weeks (though some reviewers reported issues over time).
Watching my dwarf pea puffers go into a frenzy when worms wriggle in the cone is priceless entertainment. I've developed a routine - drop in worms, give them a gentle stir with a chopstick, and watch the feeding frenzy begin. The puffers either pluck worms directly or wait for escapees.
However, the design isn't perfect. The slots are indeed too small - thawed frozen worms often get stuck, making this more of a food holder than a proper feeder. And unlike some premium models, these don't float evenly when detached.
For the price though, getting six units is fantastic. They're not high-end, but they solved my tire track eel's feeding issues immediately. Just don't expect gourmet dining - this is fast food service for fish.