Those things are good at defeating predator shields on bluebird boxes.
Are you using the umbrella type or a tube ? You can make a decent one out of pvc . Put a little grease on it .
I've been using a Kensington wobble shield for the last couple of years. An 8''stovepipe with hardware cloth at the top. It's great against 4 leggers. It worked fine against snakes the first year but by the end of last year they figured it out.
I will try the pvc and grease. I got plenty of both. Thanks
My biggest problems have been with other birds: sparrows, wrens and in one case a brown cowbird.
Do a search on bluebird houses . There's a new design now ( large oval opening instead of the usual hole ) that allows the nesting bluebird to escape without being killed ( English House Sparrows are bad about this ). You have to keep a good eye on your boxes and remove any native bird nests before they lay eggs . Wrens and Cowbirds are protected species so you can't remove a nest with eggs in it .
I host Bluebirds and Purple Martins so I trap / shoot English House Sparrows and Starlings at every opportunity . Both were imported ( not protected ) from Europe and take a toll on native birds . Look HERE
for some good ideas . You can find them cheaper but it's a good start .