For location extension we can link to Google My Business and associate *All*, *Filter*, and picked locations.
For filtered locations, we can test in UI whether the filter can return anything left. For "BusinessName" and "Label" they works fine (Show "None of your locations match this filter" if condition is not correct), but for "category" no matter that I input, it always not show this message, and in API I can only get the function (operand, lhs, rhs) but no actual filtered feed items, so does "Category" actual works when deliver?