Can We Benefit from a Caller to Islam Who Has Some Shortcomings?

It's not required for a person who makes Dawah or a teacher to be perfect. In fact, benefit should be taken from a student of Ilm (Islamic knowledge), teacher, and the person making Dawah to Allah despite his shortcomings in manners and deeds. However, that doesn't prevent from advising and guiding him to goodness using good words and in a good manner. For example, if he's being lazy about performing Salah (prayer) in congregation, he should be advised. If he is making Isbal (his clothes are below his heels), he should be advised. He should be reminded that the Prophet ﷺ said "What is below the ankles (of a lower garment) is condemned to the Fire (Hell)," and he forbade and reproached the person who made Isbal, as he said "Beware of dragging your clothes- it is part of arrogance." Also, if he shaves his beard or trims it, it should be made clear and he should be advised; you say to him: the Prophet ﷺ said "trim the mustache and let the beard grow,” “trim the mustache and let the beard grow, oppose the Mushriks (disbelievers), oppose the Majus (fire-worshippers)" “trim the mustache and let the beard grow, oppose the Mushriks.” All of these are authentic Hadeeths of the Messenger of Allah ﷺ. Also, if he is somewhat lazy about doing other forms of good deeds, not taking good care of the lesson, or other things of that sort, it doesn't prevent from benefiting from him while advising him. In short, a person with knowledge might have shortcomings; he might be somewhat careless in some aspects, whether he is a teacher, person who makes Dawah, judge, or something else. For, whose character is accepted in all its aspects!? (no one) He should be secretly advised in a good and gentle way to accomplish what was intended, and also for goodness to increase and evil to shrink. This is what is needed from the believers to do between them: advising one another “The deen (religion) is naseehah (advice, sincerity).”