They were definitely used on Mir- in 1997 one caught fire, blocking the crew's access to their escape Soyuz, though they put it out.

It looks like NASA helped redesign it to be safer, creating the modern Solid Fuel Oxygen Generator (SFOG) system still in use on the ISS as the backup.

Yes and I believe they do regularly use them on the Russian side, at least.

They were also the cause of a fire on Mir. https://en.wikipedia.org/wiki/Mir_EO-23