enormous mindless animals that will kill them instantly

Yeah, except later it turns out that the Fremen ride these animals as steeds and can control them pretty well...

There is something to this that appeals to a particular type of person (generally a male person).

This is a whole classic trope: tough, wild, free people who live in harsh open spaces. Another example is Aiel from The Wheel of Time. I guess some highly romanticised descriptions of American Indians qualify as well.

I wonder how many folks from the West really understand what they are getting into

I have a pretty large prior that they have no fucking clue.