Guvnor is free to use while you get going, and there's a Premium plan for when you grow beyond a side-round. Here's exactly what each plan includes and how to upgrade.
The free plan is genuinely useful, not a crippled trial. It gives you:
Upgrading unlocks the things you need as you scale:
Premium is a low monthly subscription with no setup fee and you can cancel any time. For the current price, see the Pricing page.
Guvnor checks your client count when you add a new client. On the free plan, once you're at 20 clients the app will let you know and invite you to upgrade rather than silently blocking you. Your home screen also shows a banner with how many of your 20 slots are in use.