Seems like a gimmick. I suppose if you could narrow down an off flavor due to a funky tank, you might want to install one. I'd just want a different tank.
If there are contaminants in my CO2, the welding supply company would lose all their commercial customers that use it in industrial processes. They need their gas pure.
It gets my vote for the most useless gimick of the month.
I be willing to bet that all it is, would be a actived charcoal (aka carbon) filter. The same thing used as a filter water. You could probably adapt a water filter and do the same thing for less money or make one yourself out of pvc and stuff it with serile cotton. Although I really don't know why you'd want to.