What is the ruling on an Imam who led the Jumu'ah prayer as both Imam and Khatib, then went to another mosque and did the same?

The aforementioned Imam's repeated Friday prayer is a supererogatory act for him. Therefore, according to the majority of scholars, it is not permissible to follow him. However, most Shafi'is hold the view that it is permissible to follow him if the considered number for Friday prayer (forty) is met without including this Imam who is performing a supererogatory prayer.