Still using the OnePlus 3 or the OnePlus 3T handset, then here is some good news. The company has rolled out Oxygen OS 5.0.3 that will also add face unlock feature on the 3 and 3T.
Face unlock was introduced on the OnePlus 5T and later added on the OnePlus 5 handset. And by default this feature is enabled on the latest OnePlus 6.
So if you are using the OnePlus 3T or the OnePlus 3 handset check for the update notification. The new update will add Face Unlock.
If you have already done that then let us know how the face unlock is, is it as good as seen on the Oneplus 5T and the OnePlus 6.