Old thread I know, but just to add a couple of points/corrections:
1. The Rolex diver extension doesn't need any pin nor tools to deploy - you simply press down on one of the links under the clasp and it pops open. The bracelet is nothing to write home about mind you, but the diver extension is actually quite neat.
2. The Rolex steel is massively harder and more scratch resistant compared to the MM300 steel. I really don't know how you could think otherwise, it's really beyond doubt. My 16610LV is nearly 8 years old and has been my most frequent wear over that period, yet it is essentially scratch-free. The bracelet has light scratching on the clasp as you would expect, but the watch body is close to immaculate. My Seikos by contrast are scratched to hell.
Admittedly I don't yet own an MM300 (thinking about it, hence visiting here), but unless it is markedly harder than other Seikos, then I expect it will scratch just as badly as my others, and that is far, far more than the Rolex.