Not had much success with the Ninja range.
Tried making biltong quite a few times, and while it results in a nice steak with an almost crispy outside, it does almost nothing in terms of the inside. It's nice to eat there and then, but pretty useless as a dehydrated foodstuff. Similar results with other things, from fruit and veg to actual meals, regardless of recipe/instruction book variations.
YMMV, but we found it tends to cook the outsides too much and doesn't go far enough to properly dehydrate anything. Might be better off trying a dedicated dehydrator.