As the restaurant name implies, their speciality is mushroom soup, and that is pretty much all you can get. The food is very delicious, and the place clean and cheap. If you are after a bowl of bakso, this is a good option rather than the roadside setups that may not have as good a hygiene standard.
The restaurant is run by some local disabled people, and you eating here helps to support their group. They also have some products available to purchase which can also help support them.