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 ‘alayhi wa sallam, is His slave and messenger.
It seems that the funeral prayer in Al-Masjid Al-Haram for the one praying is the same as his prayer in it in general and its reward is multiplied for him many times the same prayer anywhere else.
As for the deceased, the more numerous the praying men are, the better this will be for him. No doubt, praying in congregation is expected to increase in number in the funeral prayer over him in Al-Masjid Al-Haraam, not to mention the supplication for him in that place. But there is no mention of any special merit other than this.
Allaah Knows best.