Full disclosure: I've not been down this road, so I'm talking through my hat here.

Posting a project to ProductHunt is unlikely to get it in front of your target demographic, but that doesn't mean it's worthless. People will download your app and if all goes well some of those people will leave you a positive review.

That matters for ranking, which gets your app in front of people. If you get some good reviews, that matters for conversion because it lends some social credit.