I heard today in Shul that there is a custom to "skip" the first Shaar of Chovos HaLevavos and substitute it by the Kuzari or the Mesilas Yesharim instead. Does anyone know what is the source for this?
One 18th century source for this is the Noda BiYehudah (Mahadura Kamma OH 35):
אמנם ילמוד דברי תורה שיש בהם ממש...וג"כ ספרי מוסר חובת הלבבות מן אחר שער היחוד עד גמירא
However, a person should learn Torah which has substance...and also ethical work [such as] Hoveot Halevavot [starting] from after Sha'ar HaYihud, until its end.
The Seer of Lublin (18th century) is quoted here as saying that laypeople shouldn't learn it since they will not understand it..
R. Moshe Tsuriel here cites a saying in the name of the Vilna Gaon, that studying Kuzari is preferable to studying Sha'ar HaYihud.