When the MP-52 debuted this fall with its sibling the MP-62, there were two surprises. First, the company's "Cut Muscle" design of the last several years is missing, replaced with a very different "Dual Muscle" technology. Second, with the MP-52, Mizuno set out to make a more forgiving MP iron. The MP line has always been the domain of low and lower-mid handicappers. They have a reputation as being workable while providing a lot of feedback. Keeping up to those standards with a forgiving club is a bit of a tall order.
Consider that mid- and low-handicappers can be pretty finicky about their clubs. Many won't play muscle backs because they think (probably accurately) that they need more forgiveness. Others won't consider anything that isn't basically blade-like, because they refuse to sacrifice feel and workability (nothing wrong with that stance either). Forgiveness and workability are to a large extent at opposite ends of the same spectrum. Creating playable irons that meet the needs and preferences of better golfers is a gutsy undertaking for a company with a solid reputation among lower handicappers.