I read that Apple had internally experimented with it and had the Health app publish blood pressure trends and not the actual measured values, and that employee feedback questioned the usefulness of it.
Quoting from the article (emphasis mine): [1]
> As opposed to the common methods that measure blood pressure using an inflatable cuff wrapped around the upper arm, Apple's system measures the speed of the wave of a heartbeat through a user's arteries using sensors. The Apple Watch would then show a user how their blood pressure is trending, but would not be able to provide a baseline systolic and diastolic blood pressure measurement, leading some Apple employees have to raise questions with managers over the usefulness of the feature.
It's about as trustworthy as rolling a dice and multiplying the eyes
I'd definitely buy it if it were possible though... But it's not, you can only get pulse/heartbeat through that.