I am a bit at loss here. Googled at least for an hour. The usual sites (engineering toolbox etc) say that typical u-values for air cooled heat exchangers are 600-750. Most sites agree on that.

Air-cooled heat exchangers Cooling of water 600 - 750 W/(m2 K)
That is 100 - 130 Btu/(ft2 oF h).

Now I have a datasheet for a Drycooler that speaks of a U-value of around 50 W/mēK

And the following calculator has two examples listed with very different values (U Value is 3.9 BTU/h.ft2.°F) as well:

Is this because I don't understand these units or do I overlook something?