Don't have smart devices? Dont' worry! Welle is partnering with SwitchBot, a remote robot that can control all your "old" devices. Check out at http://www.switch-bot.com
Moreover, Welle also support bluetooth-enabled devices like computer and cellphones. You don't need to have a smart device to play with Welle.
Traditional gesture-enabled devices (like vision-based devices) often come with high power consumption and are affected by sun light. Welle uses sonar technology which eliminates such drawback. Moreover, some gesture-enabled devices have very few ouputs for people to use. With Welle's tracking and recognition technique, you can achieve a high degree of freedom in controlling your devices.
Echo works for a more search-like use case. For example, you ask "Alexa, play the Walking Dead season 7 episode 4", and then things get done. However, when it comes to control-like use cases such as controlling music, light and other devices, buttons or gestures in general works better. We believe these two kinds of interaction will join in some sense and better the control of smart home.
That is a great question! Researches indicate that ultrasonic noise has little effect on general health unless there is direct body contact with a radiating ultrasonic source and it all depends on frequency, intensity and duration. The technology inside Welle produces way below such limits.