I've got one. Mine's a Ninja Foodi Health Fryer Grill (or something).
You can put different foods in together, but be aware that they work best when there's room for the hot air to circulate around the food. So sometimes you end up fitting less in than you'd think.
Also, stuff tends to cook most evenly if all the 'bits' are roughly a similar size. So if you've got for example a pair of 200g chicken breasts and a load of 1cm diced carrot, the carrot would be cremated by the time the chicken is done.
I like the idea of not having to heat up the big fan oven every time we fancy some sausages or some oven chips.
That is pretty much what I use mine for, to be fair. I do salmon fillets in mine quite often; they come out extremely tender and moist but with a slight crisp to the top, very nice. Ditto cod fillets.
I also use it for chips, homemade egg fried rice, chicken thighs, sausage skewers, steaks.
I've been reasonably happy with mine. It gets used two or three times a week. The ceramic coating on the basket is chipping off though, which is a bit shit after only a year. According to Ninja, it's 'normal' and 'food safe' i.e. they don't care.