There is another advantage that they are based on and model it on the words and actions of a true righteous person--that is Jesus himself. [This fact I would not have known outside of learning Avraham Abulafia, a medieval mystic. Recently all his books were printed, but I had to go through the microfilms to discover this fact.]
The negative aspect is they deify a person.
That is to say I accept that following a truly righteous person helps one to be right with God. And that without a good example it is almost impossible to be righteous on one's own.
It is human nature to need a good example to follow--not just good words.
Not only that but if you weigh these two aspects I think the fact of following a righteous person outweighs the negative aspect of deifying that person.
Still that does not mean that deifying a person is good. Rather it is idolatry.. Still what you see in Torah is that compassion and kindness outweighs the sin of idolatry. For example you see this in the first chapter of אור צפון which is the collected talks of the Rosh Yeshiva of Slobadka. You see this also in the Talmud itself in terms of the generation of Achav when God ignored the sin of idolatry because they practiced loving kindness one with the other. But He was strict with the generation of the destruction of the second temple because even through they had Torah and Mitzvot still they did not practice loving kindness.
That being said -it is better just to sit a learn Torah, Gemara and Musar. If all that is too much, then just Musar.
[What brought this on is I see people are seeing communism does not work, Capitalism has big drawbacks. religions tend to be problematic. Since people are seeking the truth I have here set down my basic idea of what truth is as best as I can see. That is Musar is how I see things. That is I think correction of bad character and fear and love of God are the main things to concentrate on.
[I should mention that Avraham Abulafia is brought down by Chaim Vital in the last volume of his Musar book Shaari Kedusha. Also Professor Moshe Idel has done a lot of research on him. The PhD thesis of Moshe Idel was on A. Abulafia. The actual printed books I only saw after I had done as much work on that sugia as I cared to do. Nowadays you could probably order the entire set in the USA. ]