Can I connect a development or test store?

Yes, and it is a good way to look around before you use your real shop. A development store is a practice shop you can make for free at Shopify. Give it some sample orders, and nouz builds a real P&L from them. The numbers are only as good as the orders behind them. On a practice shop they are usually small and a bit odd.

Keep one thing in mind. A practice shop rarely has real costs, so its margins say little about your own business. To judge nouz on numbers you know, connect your live store instead. nouz cannot change anything in your shop, because every permission it asks for is read-only. The 14-day trial gives you time to enter your real costs and read your real margins.