Can someone explain me why it is a skill testing card? Because you can improve your draws, what almost every player can do?
In my humble opinion it's a skill testing card because it reduces the variance at least a little bit. It also makes shuffle-effects way more valuable which again results in more decisions which need to be considered, e.g. tutoring with one or more good cards on top is quite a big decision. Therefore, as the numbers of possible plays is increased the better player will more often choose the better line of play.
When it comes to the time issue I don't think that SDT is the problem, it's one of the cards which shows the problem quite clearly. The problem of slow playing players taking hours for their decisions. So all in all I vote for
UNBAN.