I'm not a fan of the niqab but have to admit, against my instincts, that it's perfectly possible to develop good relations/rapport with a wearer.
When I worked in Saudi Arabia I was able to relate very well with the young Saudi nurses who were fully-veiled, even those whose faces I never ever saw because it just happened that I was never in the break room at the same time as them.
They were very jolly girls and would come up and kiss me on both cheeks if they ever saw me off duty on the campus, in the supermarket, etc - I always knew who was approaching me by her style of face covering, voice, and gestures.
Of the many Saudi female doctors only one covered her face.