I do own a '17 Niro. The only thing we tow is a Fibco Pop-up camper. It's a fiberglass pop-up camper designed for motorcycle that weight
around 400 pounds. I would not tow really much more, as the Niro is not rated for any towing at all. Even if towing is not recommanded, with this trailer, I do respect the GVWR of the vehicule. Better than nothing....
Braking is an issue with the regenerative brake. I keep looooong distance between me and the next vehicule. Had to make an emergency stop last august, and honnestly was scared.... Trailer does not have brake.
Good point : I get 52.5Mpg WITH the trailer
Overall : Forget the Niro if you plan to tow anything weighting more than 500 pounds. And since most of FG trailers are 1000+, I guess this rules the Kia out.