a quick one

the 600 m cons
spring drive can only be service in japan
thick watch , cannot go under normal shirt cuff,
not good for desk diving, keep banging into stuff cause of thickness
as light as mm300 due to TI but still cannot wear for whole day for desk diving compare to the mm300, not as comfortable
mm300 cons
not sapphire crystal (this need to be purchase separately)
from the internet

changing the mm300 crystal

the mm300 still a winner, for a desk diver
will update again later