Yes, you can cut sweet potatoes with it. The manufacturer states it works best with potatoes, sweet potatoes, carrots, zucchini, and other firm vegetables.
The two cutting blades cut French fries into sticks of 7 mm and 9 mm. These dimensions apply to the thickness of the fries that can be produced with the blades.
This has less to do with the cutter and more to do with the preparation! Oven frites are never the same as from the deep fryer (even if you buy them frozen). But I also use the cutter to make oven frites from raw potatoes - I usually use the finer attachment. It turns out ok 👍🏼!