On the backend side:

After enabling the extension all the product will have a toggle to enable checkout for guest users.

Case1:

At admin>>Product>>if toggle is disabled

Frontend:

a.) For Example : We add “Joust Duffle Bag” in the cart. And this product is disabled from Product (Admin>Product>toggle disabled) then an error message will be displayed. If the user completes his registration then he can place his order successfully.

Case2:

At admin>if toggle is enabled

b.) If a user adds Fusion Backpack product in the cart. And this product is enabled from product  (Admin>Product>toggle enabled) then the user can place his order successfully.

Guest user successful checkout if toggle is enabled at product page (Admin) :