I tried this place yesterday after checking out this board for East Bay recs.
If I had a choice between a big chain and Red Onion I'd go for Red Onion. However, I don't eat burgers that often, so I would save any future burger cravings for a higher class burger.
For $3.25 You get a huge burger with fresh lettuce leaves(not shredded lettuce), tomato, and grilled onions, if you like. The burger is cooked on a griddle. You can add mushrooms, chili and bacon. This is a big burger that makes the Whopper look chinzy.
The fries are awful. Skip them. Fried to order, the frozen crinkle cut potatoes still had frozen spots. What was cooked was pretty tasteless.
I liked my strawberry shake ($2) and for an extra 55 cents you can have them put extra frozen strawberries in it.
It seems the days when they might have actually put red onions on the burgers are past. There was a sign outside that said "homemade pies", but they don't do that anymore.
The highest priced item was the phillysteak at $4.75. A grilled cheese was $2.65. For the price, you get lots of food. There are also hot dogs, corn dogs, chicken burgers, BLT's, chili and chicken nuggets.