How do you plan to price Ledgerleaf, an invoice reminder service?

Ledgerleaf came into being during the summer because I grew tired of following up late invoices manually. It monitors your list of invoices, sends out gentle reminders based on an automated schedule that you set and stops as soon as the payment is received. It doesn’t need any banking integrations, only a CSV export or Stripe link.

It does work, and currently, around 60 freelancers use it for free. Now I will have to start charging for it, and there I have to choose between two subscription models. One charges $9 per month and gives unlimited invoices. Another offers a free plan where users can maintain maximum ten active invoices, and after that, there is $5 fee for every 50 invoices on top of it. While the first model is simpler, the second makes more sense because it takes into account income fluctuations of freelancers.

I have now spoken with eleven users and their opinions are fairly divided, which means that I must be asking the wrong question. Perhaps the core problem is that customers don't even consider reminders worth paying for.

What do you wish someone would have told you before pricing a small utility product? As a freelancer, which of these two options makes you want to take out your credit card?