Even though the idea sounded appealing, the target audience was rather a narrow one. We needed a confirmation from the market that we'd be solving an actual problem. For that purpose we created a landing page allowing interested people to join a waiting list.
We posted about our plans in two relevant Polish groups (5K people each) on Facebook. That resulted in 24 people leaving us their emails, of which 18 have confirmed (2-step sign-up process).
Given the niche size, and the fact we posted in Polish groups only, we decided it's a sufficient proof that there is an actual problem to solve.