I'm not sure either... but I know that e.g. [here](https://github.com/spree/spree/blob/master/backend/app/views/spree/admin/products/stock.html.erb#L57) the `count_on_hand` method is called directly on the stock_item, rather than using a quantifier. But I suppose we could still define count_on_hand and using a quantifier in that method, if necessary. What do you think?

Note that this is just for a particular stock_item (and therefore a particular stock_location) so maybe it's ok to overwrite the attribute this way?