The 1906-O Half Dollar is definitely scarcer in Mint State than the 1905-O. In fact, the 1906-O is one of the toughest dates among all the O-Mint Barber Half Dollars -- only a few have smaller populations of certified Mint State examples. The 1906-O Half Dollar really shines on the high end, where a number of superb examples top off the condition census. All of the best 1906-O Half Dollars got there because of their amazing, colorful toning. Two standouts include a pair of PCGS MS67+'s from the Hugon-Shireman and Price-Duckor collections (if those names seem familiar it is because they all assembled world-class groupings of Barber Half Dollars).
Unlike most of the other O-Mint Barber Half Dollars, the 1906-O is usually well-struck and fully detailed.