I have a Yeelight smart light and I find it useful so now wouldn't be without it. At first I thought it was a gimmick but I find the tieing in the lights to come on building up in intensity a few minutes before my phone alarm goes off is invaluable as I wake up feeling far more alert in these dark months.
I also find it's good for watching tv as you can just whip the phone out whilst on the sofa and dim the lights instead of getting up and doing it.
The modes for different times of day are really well thought out too, you can have the light on in the day when it's overcast and want a bit of extra brightness in the room but it knows what time it is so when you turn it on again at night it will have a much softer redder hue than the previous blueish one, similar to what F.lux does with computer displays.