you're better off finding a good birth practitioner that supports the perenium, and is used to catching while mom is in positions other than flat on her back, during the delivery phase than wasting your money on that.
A local homebirth midwife offers it to her clients and says that some of them love it. She said it increases their confidence in their bodies, because they *know* that they can stretch to fit a baby. I poked around a little bit and the studies I read about did show a decrease in perineal trauma for women who used it. On the other hand, perineal massage (both prenatal and during labor) has not been proven to make any difference, as far as I know.
I would have loved to try it, but the $180 price tag slowed me right down!
No, it can't hurt anything, but you're not necessarily going to prevent perineal trauma by doing it. Frankly, I didn't like perineal massage and never did it after that first try. I had two minor tears during my births that were due to nuchal hands, so I feel like we did just fine. They might not have happened had my midwives not suggested I push. But then, I wanted my babies OUT, so they might still have either way.
Being in water can help keep the area hydrated and prevent tearing, I believe.
I tore horribly with my first son (although i didn't feel it..he had been crowning for a long time and I had natural endorphins plus hypnosis to help) so with our second I massaged the perineum(not "pernineal massage though" just rubbed) with vitamin E oil religiously for the 6 weeks before delivering. It definitely helped to soften my scar tissue and my midwife knew how to support my perineum with her hands and ease the baby's head out (he was sunny-side up too!) and she used warm compresses during the crowning and it felt SOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO good.