Allaah’s Messenger, sallallaahu ʻalayhi wa sallam, said, “If anyone recites, 'Ha-Mim Al-Mu’min' until 'to Him is the final goal,' and the Throne Verse in the morning, then he will be guarded by them till the evening, and if anyone recites them in the evening, then he will be guarded by them till the morning.” Al-Tirmidhi – Hadith 2144 What is the grade of this hadith?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

As you mentioned, the hadeeth was cited by At-Tirmithi in his book Sunan At-Tirmithi. It is weak, as was advised by scholars. At-Tirmithi commented on it, saying, “This is a strange hadeeth (a hadeeth or version reported by one reliable or unreliable narrator which differs in context with another hadeeth or version reported by a group of reliable narrators). Some scholars criticized the memorization of ʻAbd Ar-Rahmaan ibn Abi Bakr ibn Abi Mulaykah Al-Mulayki (one of the narrators of the hadeeth)." Al-Albaani declared it weak in a number of his books. However, Ibn Al-Qayyim wrote, "Even if ʻAbd Ar-Rahmaan Al-Mulayki was criticized by hadeeth scholars for his weak memory, the hadeeth is supported by other pieces of evidence regarding the recitation of Aayatul Kursi [Quran 2:255] and it is acceptable, despite it being a strange hadeeth.” [Badaa'iʻ Al-Fawaa'id]

In any case, it is permissible to act upon the weak ahaadeeth about virtuous deeds according to the preponderant scholarly view in this regard provided that certain conditions are met; and those conditions were previously underlined in fataawa 166199 and 13202.

Allaah knows best.