We've used it for a few years 33 gal with our pre chem.  Yields lead me to believe that the slow release is working to some extent, seem to be getting more that what you would from a normal 27%.  That said we did have 60 acres that got huge rains last summer and the N washed big time, including my injected manure test plot, so it's not bullet proof.  

Also planning to do some side by side plots with it this spring.  Famous last words.