wheel stud type extensions also ruin your turning arc (not just your turning radius). You probably don't even realize how much more effort it takes to turn your quad like that. If you went for a ride, and then bolted on a-arms to make your quad the exact same width you would be shocked at how much easier it is to turn. I was floored when I put my a-arms on, I could feel it even riding around the yard. It was easy like stock width with the rims not flipped again.
The widening kits suffer from bump steer problems. They don't change the suspension geomtery (just move it outwards) but they do change the steering geometry. They're not too bad if you're farting around on a trail but at high speeds, bump steer can throw you off your course especially if what you're riding on is uneven and one side goes through it's arc and the other doesn't.