Many practice the Tu BiShvat seder by following, reading, and singing from the kaballistic books Chemdat Yamim and Pri Etz Hadar. Unfortunately, these works have been proven to come from followers of the false messiah shabbatai zvi, may his name be wiped out. Chemdat Yamim was written by a shabbatian follower (and uses notarikons of Nathan of Gaza in the piyyutim), while Pri Etz Hadar was written by Nathan of Gaza, the false "prophet" for shabbatai who built the movement. Why then are these works still used? Are there any grounds in benefiting from them? Furthermore, can you please point to a reliable Tu BiShvat "haggadah"?
Rav Ya'akov Emden zt"l disqualifies the book Chemdat Hayamim as being written by Nathan of Gaza. Without getting into the whole debate of the validity of this claim whether right or wrong, somewhat among Ashkenazim Rav Ya'akov Emden's attitude has been the prevalent one towards the book. However, Rav Moshe Tzuriel Shlita wrote a long article on the subject and showed eighty "Gedolei Yisrael" who either praised the book or quoted from it. Rabbi Chaim Palagi, (1788-1868, Izmir ,Turkey) for example, gave great acclaim to the book. The book Pri Etz Hadar is an excerpt from Chemdat Hayamim. So we are back to square one in our attitude to this book as well. Many years ago I personally asked Rav Mordechai Eliyahu Shlita (May Hashem grant him a refu'ah Shleima) about this issue and he told me that among Sfaradim the book, Chemdat Hayamim has not been disqualified. In halacha sheets with rulings of Rav Mordechai Eliyahu Shlita , he says about he eve of Tu b'shvat: "There are those who have the custom of reading from the book 'Pri Etz Hadar'. The book Pri Etz Hadar also has been reprinted by Rabbis today. If you are in a Yeshiva, then you should consult your Rabbi as what to do. If you are unsure you may refrain from using these books without vilifying them. As far as which book to use for Tu B'shvat, I simply suggest to find an edition which has letters of approval from recognized Rabbis.