I have seen many deep groove irons and not so many single waterfall deep groove irons. I have seen few double waterfall deep groove irons, but I have seen only this single example of a completely vertical deep groove iron. Marked "Martin Watson / Special" in an oval on the back of the blade, etc., this iron has its original shaft and leather wrap grip. And it clearly stands apart from all other deep groove irons.
So why a club with vertical deep grooves? What better to have in hand should the golfer really need to impart side spin in order to curve a shot from behind a tree, etc. at least in theory.... Obviously, nobody cared for the theory.
This club is the king of the rarity hill when it comes to deep groove backspin irons! You won't find it in any other collections.