I was advised to do this when I was planning my first VBAC. The midwife stressed that best results came from beginning asap in pg, NOT waiting till the last 4 weeks. I did it & delivered without a tear, even though bub delivered face up & second stage was LONG. She also massaged the perineum whilst i was in labour.
2nd VBAC, new place, midwife said not to worry about perineal massage. I felt more confident too. Baby born under water, no perineal massage btw contractions, no tear. He presented OA though.
I certainly think you do NOT need to buy anything special to do it.