Advice Needed Link Building for Monetized Websites

Hi all,

Found this website https://3seo.io for link building, also got some good discount code for it from my friend that recommended it and it sounds good and all, but my question is...

Has anyone tried link building on their websites? (I spend a lot of time manually building links and working on on-page SEO)

Is it worth investing in such service to save time and increase authority and traffic?