I recently purchased one of these smartwatches for around $35 including postage from trademe. I had seen the same ones advertised on FB and checked on a youtube video to see an unboxing.

I purchased one for a colleague at work too. Basically It has all the usual functions for a sports band/fitbit but also included BP monitoring and Spo2.

Ill tell you what it is made of plastic for sure but it appears to work reasonably well and for $30. the connection app for the  android/IOS is an app called Fitpro. I went for a walk this am and it mapped my walk fine.

The only downside is the recordings are not automatic-on the app you press a button-"start measure"

Ill report back on the accuracy of the Bp readings-we have a cuffed one at home too.

I am on medication for high blood pressure hence me looking for this type of Device.

I have been using the Huawei G2 watch that came with my P30 pro.

you also have notifications from facebook and a few other apps.