I watched the second set of the Zverev Tsitsipas match (it was my first tennis match since Wimbledon semis) and the umpire wasn't really starting the shot clock immediately after a point. He was constantly taking a few seconds before starting the clock. The players effectively had almost 30 secs after every point. Now this could be an outlier because I haven't watched other matches but if this is the norm then it's unlikely that the shot clock is going to be a problem for players who tend to play slow. In fact it's better now because they know exactly how much time they are taking. Plus the clock stopped as soon as they started the service motion, so if you toss the ball and say sorry like Murray often does, then you can do it again without any time pressure, there is also no time limit between first and second serves. However the shot clock will definitely remove those 35-40 seconds intervals that players like Nadal Djokovic etc like to take occasionally, especially before important points. Also not all umpires maybe as lenient, I would expect someone like Carlos Bernardes to start the clock a lot quicker.