If I'm imagining what you saw correctly (like a Grandpa's feeder) that's the style where the door opens above the birds heads? That wouldn't likely happen with this style because the feed door works vertically, not horizontally. It swings inward at most about 45 degrees, with the bottom low. When it closes maybe one could get a smack in the face then?
You can put up side blinders so that no one can sneak in pecking from the side, where they aren't approaching from the front and stepping on the treadle to hold it open but "freeloading" so to speak. This is Hazel's specialty because she was very afraid of it in the beginning and now she's sometimes lazy or just does it for whatever reason, but she always backs off when the other hen steps away. So I stopped using the blinders (just some pieces of wood to block access). The medium size fits two large fowl. The Buckeyes are often side-by-side on the treadle together.
The treadle works by the weight of the bird, so very light birds might make the door too easy for a rodent to open. I think the guy advised at least 2 lbs / ~ 1 K when the Buckeyes were growing up for them to start using it. Also very small birds might require an alteration of the step, bringing it a bit closer, or capping it with a bigger step, which makes the anti-rat feature of distance less effective. Ducks need a special wide step. I think folks use it with mixed flocks; I haven't checked the latest reviews for it on that score.
I noticed the feed lasted longer when I got it going, and I only had mice and such coming after the regular feeders, no rats. It also protects the feed from rain and windy sprinkles much better. So I'm a fan.