Is there some reason you'd want gasses in a lower purity class?

(Well, it's cheaper.)

It might be more convenient to purchase pre-blended mixes for many applications. For example 90% argon 10% isobutane. In welding this would be "impure" but for ionization counting it's exactly what you want.

Fire suppression, welding gases, etc.

The only reason is cost. If you don’t need the purity then save the money.

Not only cheaper - but often also "good enough"

Is this an ad?

I don't think Linde™ needs an add, everyone knows Linde™ is the most reliable partner in producing and storing gases in all available purity classes.

(joke off, it's probably not an add, but they were excited to share the reason you see Linde on all sorts of gas tanks all over the place. It's actually quite common and if you see it once you see it everywhere. )

I've never seen Linde ever in my life (Australia).

What is funny though, at least in the Australia and UK regions, they still use the BOC brand, which is a subsidiary under Linde.

Linde was definitely around as a distinct brand in Australia before they bought BOC in 2006, but since then as you said, they now just trade as BOC.

Competitors in the space in Australia include Air Liquide and Supagas.

Supagas tend to have better prices for smaller operators, and hobbyists.

Possibly but also plausible is that its a deep joke that everyone is in on.

When googling the company, the marketing slogan that comes up is "Linde is Everywhere" but that works on so many levels. They sell air, air is everywhere. Therefore Linde is everywhere.

They are a company that sells air: that stuff that people breathe. Forget this AI nonsense. Jensen has to constantly pull something out of rear to keep food on the table. These guys sell air. What a business. :)