I live in Idaho but eat at Sumo every time I'm visiting family. The trick to making this place work for you is be selective in what you take. 90% of my plate is sushi and of that, I avoid anything with fake crab. I love their spicy salmon, shrimp, and tuna.
I find the sushi to be good, not great, but certainly good enough to come back for a few plates. I disagree, based on my experiences anyway, that it is not quite fresh. Some of the hot dishes are very good as are the salads. Desserts are not my taste so I usually pass on them.
I almost never drink anything but water when eating sushi so my tab is $12 (although I hear it's now $13) for a very decent lunch. I live a smaller tip than at a full service restaurant as all they do is clear plates and bring water. Usually 10%.
Is there better sushi in SoCal? Sure, but Sumo offers a great lunch buffet for a very fair price.