Agreed they work very well on those Nissan's DP.
But if thermos didn't work the world would also be full of dead and dying Commodores, Falcons, Toyota's and every front wheel driver too.
I have personally found the Falcon AU fan setup very reliable and very effective on my S15. Even on low speed air is pulled through both the air-con condensor and intercooler. My FG G6ET also runs a similar dual speed setup from the factory and works a treat - high fan speed rarely comes on - as the low fan speed is sufficient for most conditions here in WA. My brother's twin turbo VZ Commodore has no probs with the factory thermo fan setup either.
They key IMO is use a decent shroud coupled with an adjustable fan speed controller and from then on its a case of trial and error. Also pretty sure most manufacturers base their temps off the ECU temp sensor rather than a radiator temp sensor.
I did use a Davies Craig thermo fan conversion on my Escort RS2000 back in the day with the probe in the top of the radiator inlet, as per the instructions, and it was a total fail.