I hit the 99s and 105s and I have a very flat game but have been trying to introduce spin little by little. I don't change my grip very much at all during play, just a minor move 1 bevel or less in the right direction for the shot. My hitting partner for the last 2 years spent time with me with the 99s and he flat out told me to "buy an entire case".
It was a confidence thing, I felt comfortable taking an aggressive swing in situations where I normally did not. That sort of personal feedback is enough for me. It will not change my game monumentally, but it will add a nice element that I normally did not have in my arsenal. It might also help me to get to the net more to take advantage of my 6'4" size.
I love getting to the net but have struggle to get the right approach shot to get in as I am defensive by nature from the baseline. It allowed me to attack much more then I am used to in singles during my first set.....got my pre-order in......now just counting the days till it is strung and in my hands