The Surface Pro 3 hits stores on Friday and Microsoft is hoping it can be an iPad and MacBook killer. The appeal: A tablet with a magnetic keyboard that clips on and transforms it into a laptop. At only 1.76 pounds, it’s lighter than the 11-inch MacBook Air — the lightest Apple laptop at 2.38 pounds. The tablet features a 12-inch screen and the keyboard has been upgraded so it can be propped up at any angle, making it easier to type in your lap. The Surface Pro 3 sells for $799, plus $130 for the Type Cover keyboard.