[asavi]

The problem is that for the small percentage of texts that you only need to write "yo", there is a incomparably larger percentage that may need more than that. The Yo app removes functionality that native texting (or any number of WhatsApps and Facebook Messengers) already provide. Realistically it's like any other contact application: if you know people who use it you might use it, but I don't know anyone who uses it and I don't use it.