You can choose to show the terms and conditions checkbox only for specific products. If you'll choose that, it will only appear in the cart (page or drawer) if one or more of these specific products have been added to the cart. The Buy It Now Button Behaviour will also only work in the pages of the products you choose.
Go to your store's admin dashboard (https://your-store.myshopify.com/admin)/
Go to the "Apps" section:
3. Choose "Terms and Conditions Checkbox" from the apps list:
4. In the Terms and Conditions Checkbox dashboard page, check the Show the checkbox for specific products only option. A field will appear with a button next to it, saying Choose Products. Click it.
5. A pop up modal will appear, allowing you to choose products for the terms and conditions checkbox to appear for. Select them and click on the green Add button.
6. Click on the Save button in the top right corner of the dashboard.
You're done! :-)