ng-true-value='0' picking up wrong values

For demo see jsfiddle here and click on the Out of Stock checkbox.

It should only show stock with quantity of 0, but it is also picking up quantity of 30. I think this is becasue it is matching against string values.

I assume issue is with:

ng-true-value='0'

What is best way to fix this? Please can you provide code example?