I've never tried these supplements, and I've been told by quite a few breeders that this particular product adds no real significant improvement to your rabbit. To me, it seems that it contains more unneeded "nutrients" rather than ones that would actually benefit your rabbit.
This company also sells things like yogurt drops and dried fruit that are proclaimed to be healthy supplemental treats made just for your rabbit. But in reality, they're really nothing but sugar.
My philosphy is, if it's a brand you can findin a pet store, it's nothing but a bag of sugarat ten times the price it's worth.
And unless your rabbits are lacking in a certain nutrient, there's no need to add any supplements to their diet, and adding too much of something can actually cause more problems than good for your rabbit.