This afternoon I hit some serves with my Redondo with Topspin Cyber Flash at 24/23 kg and I am glad to mention it improved a lot.
Topspin Cyber Flash gives me better feedback and more ball bite. I was afraid it was too stiff for me but it still felt pretty soft into the Redondo. I was able to hit a more penetrating serve but performing my toss in a relaxed way is the most important aspect. When I did this the acceleration of my serve motion was a lot easier.
The only minor point is that I felt a little bit muscle pain into my underarm after a while due to the stiffer strings as I am not used to polyester strings.
5.0 level all-court player - Head IG Prestige MP -Solinco Tour Bite 19 @ 23/22 kg.