I also agree in principal that you need to fly the plane you're going to compete with.  But that said, there's a few caveats.  First, I think the Osiris is very capable TO compete with. My son is flying one very successfully in Intermediate and I know of at least one person flying it in Masters.   

Second, I think there is also merit to using a plane like the Osiris for trying out new maneuvers you're less comfortable with or learning new sequence.  And as stated above, there are times when it's the only choice due to space constraints be it flying field size or vehicle transportation size. 

The Osiris, the Wind 50 and the like are all great planes to have in the hanger for a myriad of reasons.