Got the 9.5l twin basket ninja.
Haven't missed the oven once since we got it, as it does everything we need for a meal at different heats/times synchronised to finish together.
The temperatures are reliable, no forgetting stuff, minimal cleaning (baskets are dishwasher safe), no need to preheat unless you're baking, no bending over, crouching down and reaching in for heavy tins, switches off when it's done, it's pretty much idiotproof. And far, far cheaper to run. It also just plugs into a socket, which instantly saves you a hundred quid if your oven packs up, as you're not having to pay for removal and installation. Which is more than half the cost of the ninja.
Most common things we've done have been roast chicken, potatoes, vegetables, jacket spuds and sweet potatoes, wedges, cheese on toast and bacon. Lots of bacon.
Combined with the slow cooker (which I'll probably eventually replace with a combined slow and pressure cooker) and hob, there's no need for an oven anymore.
Maybe if you have an all singing and dancing twin oven setup and cater for eight every night, it wouldn't be as great in comparison, but for us, it's perfect.