I really wish they wouldn't overload terms that they themselves invented. In Chrome, "incognito" means we don't save your local history, but it does not add to the transport security. Here, "incognito" means you've got end-to-end encryption (and presumably also doesn't save local history). Why on earth would you re-use the same term when naming two things with similar (thus easily confused) consumer-visible attribute…
Chrome: "Won't save your (porn) history"
Allo: "features like discreet notifications and message expiration" (ie, for sending naked pics)
The transport layer security is great too, but for a lot of people "message expiration" is the key feature.