Ok, I've had this for almost two weeks, that's like a decade in Paul-years.
First of all, it's a Seiko working diver. Like the SKX007 and the 6309, that means the case is shaped to fit a wrist that actually moves. The caseback is flat, and the sides of the case are sloped to spread out to full width up towards the mid-line. If you don't like nominal 44mm cases because they're too wide and dig into the back of your hand, give this or a similar Seiko a try. It doesn't dig in like a case that's full width top to bottom.
The caseback is basically flat, easy enough with the one piece case. Fully brushed finish on the back, with a polished Seiko wave in the middle. Speaking of the Seiko wave, here's the original woodcut it's based on
The watch fits my ordinary 7.5" wrist just fine. The sliding clasp is great for when my wrist swells or shrinks a bit over the day. I have it set so it's comfortable with the clasp full closed for 90% of the day. If my wrist is a bit bigger, usually right when I wake up in the morning, I just let it out a click or two. Very easy to do, almost too easy. I've noticed when I put the watch on, I need to be a bit careful or it'll open up a click or two. This is because the fliplock is also the release for the expansion slide and if I push on it when I'm putting the watch on, it releases.
There have been comments about it being a heavy watch. I've found that I'm not a fan of truly heavy watches and this ain't one of them. Almost any watch can feel heavy if the bracelet is set up too loose because it'll shift and flop around and bang into the back of your wrist and hand. The key to making a watch like the MM300 almost disappear on your wrist is to simply adjust the bracelet so there isn't a bunch of slack. Not strangle tight, but no Rolex Flop ("by God, I paid for a watch with 13 links and I'm gonna wear 'em all").
I will say, after wearing Omegas, the clasp feels just a bit tinny. Not cheap, but not a solid machined piece of steel either. The expanding section does make for a slightly thick clasp, but it doesn't bug me. The links are solid and well made, mostly brushed with two thin strips of high polish flanking the center links. Nicely done.
The crown is unsigned and that's a bit of a letdown. Mostly because I back thread the crown on every watch I have, and after a while you learn how the logo sits just when it's ready to drop into place on the threads. No such cue here. Unscrewing the crown is very smooth, as is winding. Screwing the crown down is a bit off-putting at first because the winding doesn't disengage as you screw the crown down, so you feel the winding resistance as well as the threads and gasket resisting the turning.
Casework is stunning, they just get the quality of the polished and brushed areas right. beautifully done. The shape, the curves, there's just something about these Seiko divers that have their own personality. It's unmistakeably a Seiko, and just as much a high quality watch.
The bezel is a single piece of steel, lacquered, etched, then an acrylic coat on top. Turns smoothly with the right amount of resistance, and it has a nice quality precise feel that I've come to expect from a Seiko. There are semi-big ticket Swiss makers that can't get a bezel to feel as well made as an SKX007, much less the MM300. There's no separate insert, and that's a minus for some. If you trash the bezel surface, you have to replace the whole thing. That used to bother me some, then I remembered that Omega's the same way. 2500 POs and Seamaster 300's (non-ceramic) use a separate aluminum insert but, if you scratch it up, Omega will only replace the full bezel, not just the insert. MM300 bezels run about $175-200 installed by Seiko as far as I can tell for the web, and Omega replacement bezels are $286 from O. Frei, so advantage Seiko.
The dial and hands are a high point, in my opinion. Clean and readable, and very Seiko. The date wheel looks to be black numbers on brushed steel instead of the more usual black on white, a nice touch. Lume is typically Seiko as well, and that's a compliment, they get it right.
Let's see, what else? It's a 28,800 vph movement so the second hand is smooth as an ETA. Keeping time right now at just over 4 sec/day, I'm thinking it may get even better over time.
My overall verdict? This could be my all-day, every day watch for the long haul. I like it.
/Mike
Nice "review" as well 
