Yeah, I've seen those. Two fans for about $21.50 after shipping.

And they are 5 volt.

So if there is any truth to the fan getting main battery pack voltage, it's only a matter of (short) time before the 16.8 peak voltage of a 4S pack kills them. Dont even want to think about what 6S will do to a 5v fan!

A 12 volt fan would hold up better if it's getting 16+ volts than a 5 volt fan.

And aside from the voltage issue, there is the price issue.

Two (2) fans for ~$21

or

These - Two (2) fans for $6.80

Just trying to get the best deal and longevity on what may be a disposable item with off-road dirt, dust and rocks killing the blades.