Yes, the app let's you add a custom product to the Shopify POS cart with any price you enter.
Yes, you can set a default price and then change it in the POS cart.
Yes, you can install the app and try it for free for 7-days
Yes, you can enter custom details/notes that appear with the custom product. This helps provide more details on the item being added. Ensure you have this feature activated in the app settings.