It depends on channels and HbbTV protocol they use, because there isn't only one: so, for instance, HbbTV from some German channels work, Italian ones don't, Greek ones, I don't know all: for instance it works in ERT World (I tried it by OBH, not by BH but, usually, if a HbbTV service works under one of them two, it also works by the other).
It also depend on GeoLocalization possible limits.