As for your avoiding the mosque, I see no legitimate reason for it unless the imam’s mistakes in recitation are so grave that they change the meaning, or he is an open sinner who commits one of the major sins.

So long as the only shortcoming you notice is that he does not recite with complete mastery, that is not grounds for you to abandon the mosque on his account.

Concerning your remark that he writes amulets, the ruling on amulets needs some detail:

• If those amulets contain phrases of associationism, supplications addressed to anyone other than Allah, or unknown names, it is absolutely forbidden to write or use them, by the unanimous agreement of the scholars, because they constitute associationism.

• If, however, the amulets are written with Qur’anic verses or with permissible, transmitted supplications, the scholars differ: some allow them, others forbid them, and forbidding them is the safer course. Allowing the door to be opened for writing and wearing such amulets can lead to the prohibited kinds, and writing the Qur’an in the form of amulets and talismans exposes it to disrespect and to being taken into places where it should not enter.

In short: if the amulets are written with associationist phrases, unknown names, supplications to other than Allah, or appeals for help from devils, other creatures, or the jinn, then these are associationist expressions, and whoever writes or uses them while knowing what they contain becomes guilty of associationism.

As for amulets made only of Qur’anic text, the safer path is to avoid them, leave them, and not make use of them.