Very few carts have a practical solution to the option inventory issue Mark. You have to take into account things like an option also needing to use more than one of the core product, or needing to utilise other stock items.
For example, option three = 3 off listing product plus fixing kits. Option four = 3 off listing product plus product from another listing. Option three would have to deplete the stock count by three. Option four would additionally have to deplete the stock count of another item too.
What at first seems a simple problem is actually a very complex problem.
Would be a huge task for the programmers to come up with something that is going to work in all business scenarios. Sadly there is no such thing as a
standard business need. The
solution needs to be deployable across a wide diversity of business types.