Thanks @bruce
Appreciate your feedback here on Cart Stack and after talking with @kryten we worked to get a quick update out to limit quantity of products to 1 so no more can be added to the cart, and the quantity box is also hidden:
Enable in Cart Enabler and you can also customise the above message:
This is available in Cart 1.8.5 via Sparkle updates and is a free update
Hope it’s useful 