I have the turbo maxx, the one in which the fan resides above the trailer inside the cover. I chose it because I thought it would be quieter than a fan in the vent hole (like most are), but it seems about the same sound level as a Fantastic Fan that I had in a previous trailer. I like the Turbo Maxx unit fine, but if I were doing it over I think I would get the one that pops up and down. They're just a little nicer looking from the outside IMO.
I have run the fan on mine for days and weeks on end, even while parked in the back yard. No problems yet. I have a Maxx Air vent cover over the forward vent, and the Turbo in the rear bathroom vent, so I can leave both vents open 24/7 and get constant air flow. On low the fan noise is quite unobtrusive, but like any such fan I do notice it on medium or high.