The technology used in the A&D UA-631, to measure blood pressure, has passed in a validation study, in a general population, according to a recognised standard protocol, as published in a peer-reviewed publication.
It is recommended by the ESH for self-measurement.
Longo D, Bertolo O, Toffanin G, Frezza P, Palatini P. Validation of the A&D UA-631 (UA-779 Life Source) device for self-measurement of blood pressure and relationship between its performance and large artery compliance. Blood Press Monit. 2002 Aug;7(4):243-8. PMID: 12198341.
ESH-IP:2002 - Pass General population
Ware A, Stevens R, Selwood M, Fleming S. Accuracy of blood pressure monitors available in high street pharmacies. Blood Press Monit. 2016 Feb;21(1):59-61. doi: 10.1097/MBP.0000000000000151. PMID: 26427055.
Measurements from the A&D UA-631 are compared to those from the Omron BPM tester PA-350, though not in a formal validation.