Learning Musar [works of ethics of the Middle Ages  like The Duties of the Heart helps to gain physical and mental health. That is what Isaac Blazer said. He was a disciple of Israel Salanter and we can trust that he knew what he was taking about. 
But this takes  a lot of faith in the wise to believe this. There are plenty of world views out there that claim that fear of God is not even a worthwhile goal. And among people that agree that fear of God and good character traits are worthwhile goals there are many opinions that learning Musar does not help and that there are better ways. From what I have seen all  of these alternative claims are false. {And many of the alternative approaches are negative and harmful.} That is based on my experience and observation.
So while learning Musar has limited capacity, at least it does something positive. It may not work magic but we can trust Israel Salanter and Issac Blazer that it has positive benefits. And it benefits far outweigh the benefits I have seen from alternative paths.

The difference between the Musar Movement and I is that I think people should spend an equal amount of time on Medieval books of Philosophy like The Guide for the Perplexed,  and Saadia Gaon's אמונות ודעות (Faiths and Doctrines). This is because I don't think good character is independent of a good world view. I think rather that good character depends on a good world view.

There will be noticed some areas in which the world view of Saadia Gaon and Maimonides are not in accord with the Kabalah. This speaks more to the detraction of kabalah as a source of information than the reverse. Mystics can be very helpful with their insights but can't change the world view of Torah. Knowledge gained by mystic experience remains mystic.
The major philosophers of the Middle Ages with the approach of the Talmud and Torah are Saadia Gaon, Maimonides, Maimonides's son Avraham, Ibn Gavirol, Isaac Abravenal,
Yehudah Abravenal . If one does not know at least what they say it hard to imagine that anything he says on the topic of Jewish world view could be valid or interesting. If one has done the homework then his views can be interesting but not before.
I should mention I hold from the natural law approach of Saadia Gaon and Maimonides-so I respect any system that I feel is striving for natural law. But I have no tolerance for systems that I think are tilting people towards evil.