Following in the footsteps of Avenged Sevenfold, Northlane surprised its fans with a new album called Mesmer, and the sales numbers didn't turn out so great. The band's 2015 album Node sold 3,500 in its first week, while Mesmer only sold 1,800. Granted, Mesmer was a lot different stylistically than Node, and we all know how well stylistic changes can potentially do for a new album's sales.
So does the surprise release work? Ask Avenged Sevenfold, who sold 72,000 copies of The Stage in the first week. Metal Insider points out that while that number isn't awful, comparative to the previous two albums, the band sold less than half of what it normally sells. Furthermore, The Stage to date has sold 169,000 copies, which is just over what the 2010 album Nightmare sold in its first week.
So maybe there's an art to the surprise release that metal bands haven't hit on yet, or maybe it's just not the way to go.