The impurity levels we are talking about are minuscule. Usually just nitrogen. This matters in the formation in the head of a beer or the mouthfeel of a soda. Adding a few moles of hydrocarbon or nitrogen to a tank is not going to be effected.
I’d been getting my refills from a welding shop for years . When I asked them about food grade they looked at me like I had just sprouted a second noggin. Since they closed I do now get food grade from air gas. No difference that I can see.
Side note, most co2 sold is of food grade purity regardless where purchased. There are only so many wholesalers of gasses.
The benefits i have for using NuCO2 at work are not related to its purity but logistics. They use sms alarm for automatic refills, the tanks are permanent installs, no more swapping out vessels that may fall, and they integrate co2 leak alarms during install.
Yes they market that its more pure, but the safety and no need for an employee to verify volume is why I use a service like this.