Thought I'd pass along to anyone else that needs to do this that this $29 wrench set on E-Bay includes the wrench you need to get insert nut off. It's made of 1/4" plate steel. I questioned whether it would be stout enough, but it was. I used a long handled 1/2" drive ratchet with a short extension. The other wrench in the set is useless for this, but maybe you can use it on your ATV.
https://www.ebay.com/itm/232699396780
Probably doesn't work quite as well as the $300(!) German one, but it got the job done for me.