yea i think MBTI has simplified jungs psychological types way too much, but it has also added some really valuable sides to it. imo its best to look at these three as different sides of a same thing. jung owns, but it has its shortcomings also
Okay, I concede that all three serve a useful purpose. "Please Understand Me" could at least stop people from believing that those who are different from themselves are "stupid" or "crazy" or whatever. It at least does that, and I do think there is truth in the core Promethean NTs wanting power (or to be right, or appeal to authority) and Appollonian NFs want to find themselves (and are more likely to go into therapy than other types, apparently) etc.
However, it annoys me because it leads to harmful stereotypes that don't really do justice to how personalities can manifest in ISFJs or ENTPs.
MBTI does more at least, IMO, to stop people from thinking in stereotypes so much, but it still doesn't touch on the depth and complexity of motive in Jungian theory.
Then again, Jungian theory is more subtle to grasp, it can get confusing to some, and you may have to really be honest with yourself and/or observe others over a period of time instead of being able to instantly slap a label on them according to behaviors.
So maybe it's good to start with Keirsey and MBTI and move up to Jungian theory. It's just that sometimes people get stuck in Keirsey and go around saying stupid shit like "all ISFJs are frigid prudes."