The protective lens is the wear part that decides how much you see. Spatter frosts the polycarbonate, and through a scratched lens a welder instinctively leans closer to the pool and breathes in more fume. Keep a bulk pack in stock and change the lens as soon as the view stops being clear, not when it stops being usable.
The inner lens protects the filter on the face side from moisture and from spatter in overhead work. It costs a fraction of an ADF filter, so leaving it out is the most expensive saving in the whole set.
The ADF filter is replaced rarely but has to match the helmet and the work. Look at the optical class to EN 379, described by four digits such as 1/1/1/1, and at the switching time. Good filters darken in under 0.1 milliseconds, cheap ones can take 0.5 milliseconds, which you feel in your eyes after a day. Check as well whether the filter detects a TIG arc below 10 A, because not all models do.
Headgear and headband decide whether the helmet can be worn for eight hours. Replace the sweatband regularly, because sweat softens the plastic and speeds up cracking of the catches.