If these tools have been useful, sharing them is the single biggest thing that helps a brand-new, one-person site grow. Your link is tagged so if someone signs up for Pro after clicking it, that shows up in our records, meaning we know it came from you.
A genuine recommendation works better than a mass post. Good places: a reply to someone asking about invoicing/rate-setting tools in a freelance forum or subreddit, a mention in a newsletter or Discord you run, or just sending it to a freelancer friend who complains about chasing invoices.