B. Kumar is a swing bowler so I agree the best of him will come on the fast, lush green pitches. That said, he isn't as slow as Praveen Kumar and has variety in his bowling as well so I don't think he will struggle as much as Praveen Kumar did on flat wickets. Umesh Yadav is all about pace and accuracy so he is a different kind of bowler altogether. He is one bowler who did bent his back against England before getting injured at that was pretty spin friendly track at Ahmedabad with no help to pacers whatsoever. I think these two lads, Yadav in particular, will go a long way in being a pivotal part of India's pace attack.