To the best of my knowledge, Hizb Al Tahreer doesn’t follow the manhaj of Ahlu Sunnah.
Whoever claims that khilafa is superior to salah is ignorant and must be brought back to his senses. If he refuses, he is not a Muslim.
This Hizb or party is focused only on politics and has nothing to do with Islam. Therefore, such people should be avoided and one should only stick with real practicing Muslims.
Muslims in the west should follow the leader of the Muslim community who acts as their leader and Imam. They can also follow one of the Muslim leaders in Muslim countries and this would be sufficient.
And Allah knows best