[msrenee]

Mustangs behave pretty much the same as other horses when confronted with something scary. They're not really any different to work with than any other unhandled horse. Mustangs are not wild horses, btw. They're feral horses descended largely from the horses of the Conquistadors.

[mannykannot]

So much for my guess! BTW I am well aware that mustangs are not wild horses, which is precisely why I made the distinction in my original comment. When you say "any other unhandled horses", are you including truly wild horses?

[monocasa]

There arguably aren't truly wild horses anymore. The closest, Przewalski's horse, only exist in the wild as a population reintroduced from captivity. The captive population that they were reintroduced from very might well have been a more docile subset of the subspecies, making your question difficult to answer.