I usually buy a basic version of the sauce, and most of the time I use Kikkoman's Memmi.
The Memmi sauce is concentrated and needs to be diluted with water when you use it. On the packaging label the ratio of the sauce and water for making different bases/sauces such as udon soup base, somen/soba or tempura dipping sauce, and many other uses. When I use it as a mochi dipping sauce, I don't dilute it at all. It's yummy.
Gotta have a bottle in my fridge at all times!
I found this somen (Japanese thin and white noodles) the other day.
The somen noodles cook in 3 minutes! After the noodles are cooked, run them under cold water and strain completely before serving. A lot of times people would put a small bamboo mat underneath the strained noodles to make sure no water "stays" with the water. Use the Memmi (1:4 ratio) as a dipping sauce. Some people like to add grated ginger or chopped green onions to it.