Ninja PB051 Single-Serve Coffee Maker vs Keurig K-Duo Coffee Maker

Buy the Ninja PB051 if you mostly drink single cups and want grounds flexibility plus a built-in frother for lattes and iced drinks. Buy the Keurig K-Duo if you regularly brew a full carafe for a household or guests and want a large shared reservoir and programmable Auto Brew. The Ninja is smaller and lighter, with more single-cup sizes and four brew styles; the Keurig adds a 12-cup carafe side, a 72 oz reservoir and a hot plate. Owners of the K-Duo line report solid everyday reliability but a bulky footprint, while Ninja single-serve owners praise the frother and pod-or-grounds choice.

• Choose the Ninja PB051 if you brew one or two cups at a time and want pod-or-grounds flexibility, a frother and iced-coffee settings in a compact machine.
• Choose the Keurig K-Duo if you often need a full pot for several people and want one reservoir feeding both a carafe side and a pod side.