Yes Chris, I would avoid any cleaner with a G rating for emissions if I had any respiratory problems. Most of the Hoovers have very mediocre performance, something I have learned first hand today with my new unfortunately named Hoover Eco G. I think the G stands for Globe, but after using it, it could be its average performance rating. It's nice to use, but very noisy and very poor on hard floors with an average pick up on carpet.
I'm glad the rating system is being introduced because it makes it easy to compare different models.
I personally will not buy a new cleaner unless it's A rated in most tests. I don't mind a B or C for energy use, but I would want A for pick up on carpets and floors.