As for which ones are reliable - they all use a variant of the ADUM datasheet app circuit, so there's probably little to choose between them (apart from maybe DC-DC converter wattage). You don't say what part of the isolator is getting hot, but it sounds as if it got back-driven with greater than 5V when your Duo smoked. Each side of the isolator is separately powered to maintain isolation. The switch will be there to select the slew rate to match USB low speed or high full speed (the opto is there to mirror the same setting on the other side). It's worth downloading the datasheet to understand them, the pin functions are very simple. All of these isolators use Analog Devices ADUM3160 or ADUM4160 isolator ICs.
