We've eaten there a few times... most of the time it's late, and nothing else is open... after all, these donburi shops are usually open 24 hours a day!
Another donburi chain that we see quite a bit in Osaka was Nakau. There's one in Nakatsu (near Umeda) that's really close to the hotel we usually stay at.
Beef donburi is a must-have in donburi shops.
The food at these shops are not super fantastic, but it is like simple home-cooked meals... plus it's always available... and that's a very good thing.