The fact is that most people don't floss... probably because they find it too fiddly and awkward to use, but floss is an excellent way to clean the gaps between your front teeth and if you already floss you should continue.
The problem is that Gum disease and decay between the back teeth is a much bigger problem than the front teeth... as evidenced by the millions of people who have missing back teeth but still retain the front ones. Interdental brushes address this very important issue and they can be used with one hand, which makes cleaning much easier. This also means they are more likely to be used. They are also better at cleaning the indents or hollows between the roots of your molars and pre-molars. These areas are called furcations. Floss forms a straight line across the top of the furcation, whereas interdental brushes have bristles that spring out sideways to clean the hollows and the bristles also massage the gum line, promoting good oral health.