I used to use it... then Fidget developed a very severe liver infection and I very nearly lost her!!
Anyway... While i was trying to figure out what could possibly have caused the infection I came across the multitute of literature with reference to rats developing liver problems due to a toxic byproduct when their urine reacts to the chemicals used to treat woodshavings... whilst skimming this I found a couple of references to rabbits and the same issues arising. Even there is no solid evidence for this to apply to rabbits aswell, i believe this may have been what caused Fidget's liver infection. I instantly stopped using it and she recovered and it has never returned... in any of my buns!
Of course this is just my opinion as there is no conclusive research but it is enough to open my eyes anyway!