I must confess that this is my favorite Japanese restaurant outside of Japan (mainly the Tokyo/Yokohama area where I frequent). I usually go there for lunch so I don't really get the opportunity to eat izakaya-style so I have a different viewpoint of this establishment and I'll limit my comments to the family-style, fixed menu items.
My preference, even in Japan, is more for family-style meals unless I'm out drinking with my friends with plenty of time (and expense account money) to spend. I prefer to go to sushi-ya, tonkatsu-ya, and curry or ramen shops when I'm in Japan. That's just my personal preference.
Anyway, my wife talked to one of the owners recently and we found out that virtually everything there is made from scratch, including the miso soup and the ponzu sauce that they use on the Hamburg Steak meal course.
The Hamburg Steak meal is my favorite by far. Anyone who has never had it should think about trying it. A very flavorful large Japanese (plenty of preparation went into this) hamburger patty with a large heaping of oroshi (ground daikon radish) flavored with their home-made ponzu sauce and ground red pepper seasoning beside a finely-shredded pile of fresh cabbage. The combination of the meat, oroshi, ponzu, pepper seasoning and cabbage is fantastic, as good as anything that I've had in Japan.
The tonkatsu is extremely competent (again, everything made from scratch) as is the saba shioyaki (grilled mackarel). The daily lunch specials are also extremely tasty and very well-prepared.
I have not been to Tanto so I can't make that comparison but the owners at Saizo cater to the most fastidious Japanese restaurant customer, the visiting/expat Japanese salaryman first and the expat salaryman's wife and family second and they seem to do a pretty good job of bringing back repeat business from this customer base with virtually no advertising except for word-of-mouth referral.
I think the Japanese customers appreciate the made-from-scratch offerings, because it's truly home-style cooking like their grandmother used to make for them back in Japan.
Someone here commented about the Mexican assistant chefs. Personally, this doesn't bother me because I've watched them from the counter (it's an open kitchen) and they've both been there since I started going quite some time ago and they are obviously very competent in what they do and are always working under the supervision of the owner. I believe that many fine dining establishments (not just Japanese) employ Mexican chefs with great success. The key is to have the head chef who keeps an eye on everything.
So, again, I give Saizo two thumbs up and appreciate having authentic Japanese food available in Sunnyvale.