The diagonal works EXACTLY as advertised. The description specifies refractor or catadioptric reflector. It's not designed nor sold for Newtonians, hence the 1-star rating should go to the other reviewer for his failure to READ and not to the product.
This item will not focus an image on a Newtonian reflector which had to be returned. It did not work with any eye pieces 25mm or 20mm and more powerful through 4mm of course on a Celestron PowerSeeker 114AZ.