Also worth checking your cars accessories socket can supply 200w. They usually say on the cap. If not check the fuse box for the fuse size (will need to be 20a+)
It'll work initially but it puts a lot of stress on the components. The engineers assume each component will receive a certain measurable VIR/PIV curve - a square wave is just turning the power on and off, this leads to a ton of stress on the components (think jamming a car in full throttle and breaking over and over again).
This is a sinewave inverter, it's just s square sinewave. Pure sinewaver inverters do cost a ton of cash. It's basically down to what you want it for. I wouldn't in a million years put a high end Dell or Macbook pro on it.
It'll work fine until it goes bang. Pure sine vs square wave leads to some seriously unhealthy wear. You can actually hear it on most devices, it'll have a wine or some other artefact as the capacitors and conductors are not able to balance the current. Just avoid charging sensitive equipment and it's a steal
If your kettle is 200w or less all that will happen is you'll be stood round for ages waiting for it to boil.