My flip phone (ZTE Cymbal running Android AOSP 5.1.1) doesn't have an option for a voice assistant, and I don't care or need one. I have stated many times in the past, that it was a cute novelty for a short time, but then became more a hinderence than a useful feature.
I had a short stint with IoT devices that ended whenever Google couldn't 'talk' to a smart bulb or something and it became never-ending frustration and I just gave up and do my automation via timers now, and use incandescent bulbs (I recently found that LEDs are harsher and give me migraines) and am more fond of vintage over modern these days. I remember Assistant having many instances of me having to ask her twice to do something like 'turn on the living room lights' to having half the lights come on, and then she spits out 'sorry, living room light 3 isn't responding right now' and then I couldn't turn any of 'em off because she lost the link. It was too hit or miss to have any confidence.
Don't get me started on Alexa having the 'there are two or more devices with that name, which one did you want?' (sorry, Alexa, there's only ONE light by the name 'living room light one')
But it was cute to get bad jokes out of S-Voice on my SIII. I do miss her HQ english female voice pack (very sultry sounding). The novelty lasted an hour and that was it. It could do some things Google Now at the time could not though, such as toggle Wifi and Bluetooth on or off.