We do a weekend market stall as well as the shop. Can I take a second tablet there with the same POS?

Yes. Pair another device under Settings → The POS and take it with you, because there is no limit on devices and no charge per device. It works like a POS for a food truck: mobile data or no signal at all, with sales kept on the device and sent when it reconnects. With no printer, pressing Print shows the receipt on the screen, and you can send it to the customer on WhatsApp. Open a shift on that device with its own float, and close it at the end of the day with its own Z report. The POS and the counter tab in the docs covers selling with no internet.