TOKYO -- Last week, Masayoshi Son addressed a nearly empty room at a conference in Saudi Arabia. By contrast, when the CEO of SoftBank Group presents his company's earnings in Tokyo this week he will face a barrage of questions. One may even be: Was it all worth it? It was almost exactly a year ago that Son floated Softbank's mobile unit in Japan's biggest-ever stock market listing. Son used the placement, which raised 2.6 trillion yen ($23 billion), to pay down debt, buy back shares -- and fund high-tech bets by his Saudi Arabia-backed $100 billion Vision Fund.