The Meshichists give Chabad a bad name. They are like those 10 people making tons of noise in an extremely crowded room, making it seem like the entire room is rowdy for someone who comes in and immediately runs out because of the ruckus.
These animals came in not just the last generation of Chabad, but even at the VERY END of the last generation. It is no thanks to these guys, that the GOOD NAME that Chassidus bought itself over CENTURIES was tarnished and practically brought back to where we started, over 230 years ago.
The original war against Chassidus was due to many, many misunderstandings and tons of false accusations. By the third generation of Chabad Chassidus (led by the Tzemach Tzedek), all the original issues the Jewish world may have had with it were solved. The questions were answered, and peace was held. The ensuing battles were mostly fought together by all of Orthodox Jewry against the haskallah movement, and the antisemitism that reigned.
That being said, Tanya was written by the first Rebbe of Chabad, so following the period when the orthodox Jewish world made peace with Chassidim, there is no official view that negates its authenticity.
Next point: the entire point of Chassidus is to bridge the various parts of Torah - the PARDES (pshat, remez, etc.) in a way that makes everything clearer and more relatable. It is NOT, as is a common misconception, a "distilled version" of Kabbalah. Much to the contrary.
Learning with a Meshichist, I would highly NOT recommend, for the most part, for one simple reason: from my 7-8 years being ALL OVER various Chabad communities, yeshivas, etc., I have seen that for the most part Meshichists have a very feeble, extremely shallow understanding of Chassidus, and in general learning with one will not bring justice to the depth and richness that Chassidus has to offer. Again, I speak with experience.