AGNC Investment has an ultra-high yield, but if you are an income investor, you probably won't be interested. It's a complicated story.There's nothing inherently wrong with AGNC Investment (AGNC -0.31%), but it isn't a simple company to understand. So if you see the real estate investment trust's (REIT's) huge 14.7% yield and think you've found an ideal passive income stock, step back and take a deep breath. AGNC Investment isn't really for you. Here's why.A few charts tell the AGNC Investment income storyB ...