I gather that as of summer 2015, Malta has introduced a stored-value card for use on buses, much along the lines of London's Oyster card or Hong Kong's Octopus card. The Maltese version is called a Tallinja card.
Looking at the bus fares table, a single journey on the bus is only 75c with a Tallinja card, vs €1.50 (winter) / €2 (summer) if bought with cash on the bus. So, it looks to deliver a decent enough saving to be worth getting for even short trips!
However, I can't seem to find anything on the Tallinja card website about being able to buy one on arrival at the airport. As an arriving tourist, is this possible, and if so how?