I have this. It's ok but you get wildly variable readings if you don't keep your forearm perfectly rested and flat on a surface. Even then it's going to vary a lot. Wrist based blood pressure readings are never going to be that precise unfortunately
For all wrist BP monitors the wrist must always be at the heart level, not flat on the table. It won't change the amount of noise in the measurements, but it will remove the bias.
> you get wildly variable readings if you don't keep your forearm perfectly rested and flat on a surface