I've just finished running it for four 4th level characters.
I've added an encounter at the beginning and we completed it in 3-1/2 hours.
During the final battle things looked very grim for the sviferblin warlock, as he found himself surrounded, but his imp familiar killed a cultist (striking from invisibility), the gnome endured 3 attacks of opportunity and he saved himself...
Overall, nice and enjoyable. All the players absolutely loved the map.