I used to have a factory roof-mounted for one of my pop-up campers, although it was limited to 2 bikes because of the roof air conditioner unit. I took that set-up across the Rockies and through Montana, including Missoula. My concerns regarding a roof-mount on the Explorer (or any car or SUV) would be the added wind resistance, remembering your overhead clearance, and the plastering of insects and road spray you're gonna get on them at highway speeds.
Of course there's wind turbulence around the back bumper, too, and they don't put rear-window wipers on those vehicles for nothing. In rain you can expect your bikes to become caked with grime in every crevice. Have you considered a totally different solution, of putting a hard-shell luggage carrier on the roof, and putting the bikes inside the SUV? You can do that with a temporary rack, same as for the bikes. An aerodynamic carrier might create less wind resistance than the bikes, Again, depends on how many bikes you have, and if you'll have backseat passengers.
Otherwise, I'd recommend a rear rack, though I don't know all the brands mentioned. Selecting one with a good web site for assuring a proper fit would be a consideration for me. You might find they have instruction/owner's manuals for download in pdf, to get an idea how their mounting works on your Explorer. And have you checked if Ford itself recommends anything?