My wife and I stayed at the Tavistock in August 2017. She had stayed there many years ago and found it fine. By 2017, we found the Tavistock a bit old. The breakfast is not excellent. It is stodgy, and lukewarm for the hot items. In August, there was no air conditioning. And the rooms were small. My wife thought they were cut in half from what she stayed in during the seventies.
It's noto a bad hotel and you can catch buses and subways to the theatre district and the rest of London. Just don't expect too much.