We stayed in the GB this summer and I recognize some of the images of the demonstrations as being right at the hotel.( The Parliament building is right across the street). I think a lot depends on just when you are going although the demonstrations and strikes are unpredictable.

If this is just a leisure trip I know I would rethink going to Greece at this time....if it is business I might consider moving to another hotel outside the Syntagma area.

You might also want to read the TripAdvisor forum on Greece.... there are numerous posts of people on the scene.

BTW... the hotel is not " near" Syntagma....but directly on it!