I bought a GroundHog Maxx ATV disc a few years ago and it worked great, especially on small, odd shaped plots that are hard to reach with bigger equipment. The width of the implement is pretty small, but you can fast with this disc and that makes up for it. I liked how this design used the weight of the ATV to dig into the soil. They are built like a tank, which can be a problem if you have big rocks because the disc is likely stronger than the ATV and you can bend the hitch on the ATV like I did. If you have big rocks, I wouldn't recommend the GroundHog Maxx, but if you don't have big rocks it works awesome.
I bought a tractor, so I don't use my Groundhog Maxx disc anymore and would sell it for $225 if you wanted it. I believe I paid around $375 for it and I probably used it less than 20 hours.
I have a friend who bought one of the pull behind King Kutter ATV discs, but to cut into sod he needed to weld a carrier on top that allowed him to add cement blocks for weight. I believe he paid around $600 for that disc and he said it worked pretty well once he added weight. He also had better luck spraying the sod to kill it off before trying to disc it up.