Musar after it got mixed with kabalah takes a different direction than the Musar of the early Middle Ages. For example the attitude of the Rambam and his son's and grandchildren's Musar books have very different attitudes than later books of Musar. A lot of fanaticism gets introduced after the Middle Ages.
This can mix up people.
However this is not to imply anything negative about the Ari (Heaven forbid.)
My feeling about this is that if one feels ready to learn the Ari (Isaac Luria) and has been through Shas a least a few times, then the best thing is to learn the Ari straight. [The main thing I think is the Tree of Life though my learning partner, David Bronson, thinks that the מבוא שערים is even more essential.]
But whether Gemara, or the Ari, the problem is always that cults try to gain respectability by using these names to lend to themselves a air of legitimacy.
[Though I am myself ashkenazic, I can not stress enough to avoid all the ashkenazic sitra achra [dark side] books of mysticism written after the 1600's.] The only commentary on the Ari from the ashkenzic world is the Gra. So for good commentary on the Ari, the best thing is the Gra, Rav Shalom Sharabi (Yemen) and or Rav Yaakov Abuchazeira.
The truth be told I do not think it is possible to get the "spirit of Torah" outside of a Litvak Musar yeshiva. I have absolutely no respect for synagogues at all. If one is not in the area of a genuine Litvak yeshiva then the best thing is to learn at home.