The Amazon Echo Flex is essentially an additional listening device that you can add around your home so that you can access the various SMART features of Alexa.
You can turn on lights, adjust thermostats, lock doors, and more with compatible connected devices. What it will not do is act as a replacement for a Smart Speaker as the tiny speaker is not designed for music playing though you could connect a speaker via 3.5mm aux, Bluetooth, or setting your Preferred Speaker in the Alexa app.
You can connect a nightlight or motion sensor attachment (each a $15 extra) via a USB port.