Bluebirds, in my opinion, are most attracted to nestboxes. Put one up and see if they find it. It takes work to get them to find your meal worm feeder. And that particular feeder take more time then some of them. I feel the grid/jail style feeder is easier for them to navigate initially.
Several of us drew bluebirds to our yards by putting up a nestbox. Then we introduced and offered mealworms in a clear or white smooth sides glass type of shallow dish. A mealworm feeder was our last step.