As a hobby project I made an online calculator for estimating dosage in cannabis edibles (https://www.scientificedibles.com). I found it quite a challenge to get users/feedback initially, however I became active in the edibles subreddits on reddit. I generally try to be contribute to the community, and when I see questions where my site can help I do the calculations for the user, and post them a link to it on my site (I made a sharing feature).

I think this is a fair way of providing value, while also raising awareness of my project. I think you can easily get in trouble if all you want to do is just get users to your site by spamming links, and not put in any effort to understand the community you are engaging with. I would just go with ads instead if that's the case.