The 1907-O Dime is just about equal in rarity to the 1907-S. The 1907-O is not as rare as the 1907-D, but it is much scarcer than the 1907-P. High grade examples are somewhat plentiful and can be found with relative ease in all grades up to Gem condition. MS66 examples of the 1907-O Dime are almost as plentiful as MS65s, but in MS66+ and better, this date becomes exceedingly rare.
In general, this date is well struck. Collectors should focus on obtaining nice, problem-free examples that have colorful toning.