The ball feet are a great addition to your camping set-up helping to make your Helinox chairs that little bit more stable.
Helinox says:
Get a more stable seat with this set of 4 ball feet from VIBRAM rubber and designed to prevent your chair feet from sinking into soft ground or sand.
Helinox's Vibram Ball Feet are really solid once you have them on a Helinox chair. You get a more secure feeling expecially on harder ground where camping chairs can be a bit skittish. The vibram feet are made of good quality rubber so will last a good amount of time.
If you are already carrying a camping chair then weight isn't the biggest priority but for improved performance on less stable ground, you can't go far wrong with these.