Oh, they use it to gain goodwill, attract talent, and get free labour. It’s no secret. Zuckerberg openly talks about this.
I wouldn’t call it bait though. They’re legitimately good projects, and you’re free to make use of them while giving nothing back.
I imagine they would have the same eating experience as those mini shrimps commonly used in Chinese cooking. Meaning, great tasting but very unpleasant texture due to the shell.