I definitely like this iteration the best of all. Like all tour90s, it just punishes the ball and forces you to anticipate and setup early. But i love the feel on this one, much more so than n,k or b.
I use the 90 to practice with, helps me focus on fundamentals, getting the ball in the middle of the stringbed and really grooves my serve. Then i pick up my regular sticks and watch the racquet head speed bump up without too much breakdown of technique.