There’s a limited-time sale on the Double Stack XL, or DoubleStack XL, as it’s known in the US. The Double Stack XL is the brand’s newest air fryer – and its unique design makes it a good buy for people who can’t find the kitchen counter space for a standard dual-drawer model. Still, the fact that it’s new, innovative and capacious means that at £269.99/$229.99, it’s the priciest Ninja air fryer model, so you may not have been tempted to buy – yet. But now is the time to go for it as, for a limited time in the UK, Ninja is offering 20% off the Double Stack if you buy direct from the brand, sav…