I don’t know which cable you’re referring to. The only one that kinda looks like that is the aquabus cable, which you’d use to plug in to an aquaero or similar. But that removes a chunk of features from the sensor.
That’s correct. Connect the cable to the power switch header on the motherboard and then plug the powerswitch lead into the female plug on that lead. The other end goes to the signal connector on the sensors. You can use that plug as either the fan signal or the switch signal, not both.
This is one of the reasons I'm looking into one of these for peace of mind. Though I'm debating on this or the Bykski version. Though, from what I've read the water quality reading is only useful if using Aquacool's coolant? That and trying to find one in stock is another task in itself.
I'm not sure about the water quality. Whilst I was finishing off my build during periods of using only distilled water (or diluted coolant) I saw the water quality fall from 100%. However when it was complete and I refilled it with fresh coolant (I'm using EK Cryo) it went up to 100%. It's still showing 100% now. I have no idea when I will change my coolant - I have seen various recommendations - but I certainly will take note if the meter water quality drops from 100%.