It’s cool it worked for them, but surely cheesy crap like this has got to succumb to the law of shitty click-throughs almost as soon as it starts right?
Yeah. It’s a clever technique, but I wouldn’t expect it to last too long or produce very high-quality prospects. There isn’t even any step enforcing that users leave a comment, and they’ll catch on in the next few months in much the same way it took a few months for almost all of Facebook to tire of viral game loops. (Even setting aside that LinkedIn should ban the practice.)
The users are folks who were interested in a single lead magnet and open to viral nonsense, so they’re not well-qualified as being interested in the topic. I’d want to immediately put them into a sequence to ratchet up their engagement. Perhaps a webinar, or more likely right into a <$10 product. Make the pipeline strict and unsubscribe them if they don’t progress through the funnel so you’re not paying your mail host for near-worthless subscribers.