I love my mini oven. Compared to my conventional oven, it uses WAY less electricity, yet cooks small-ish things very nicely indeed.
When I bought it I could've bought a slightly larger one with a rotisserie function for a few pounds more but wasn't sure about the concept of the mini oven at all, so went for the cheaper one. In hindsight, I wish I'd bought the other one, but even so, I don't regret buying the one I have and don't plan on replacing it.
OK you can't cook a turkey or a giant batch of biscuits on one, but how often do you need to? If you have the space, keep the big oven available, but switched off at the mains, then if you ever do need to bake six cakes or roast a giant turkey, all you'll need to do is switch it back on and take out all the baking tins and chopping boards you've been storing in it.
I regularly bake a small loaf cake in my mini oven, or half a dozen cupcakes, muffins or biscuits. Also make my own rissole/potato cake types of things, salmon in puff pastry parcels, reheat flatbreads I've made on the (induction) hob, etc. Mine has a decent grill too, so I can easily get a nice crispy top on stuff I make or reheat in the microwave, grilled fish etc.
I have needed to buy more small tins and dishes for it, though, than I needed to buy new pans for the induction hob!