Its just a case of deriving opinions from limited anecdotal evidence! :)

I've had 3 122 or 544 cars - and not a single one still had a surviving original temp gauge (the one on my current 544 'works' - but goes straight to red as the engine warms, its disconnected and a secondary gauge installed in its place). And of the 4 1800E/140 series cars I've had I never had a problem with either the gauges or the voltage stabilizer. And when the gauge fails in a 140 series it has several independent parts, not the expensive single unit. But my analysis suffers from limited sample size.

Once, on my long gone '63 122 I swapped in a 140 series GT Rally instrument cluster (long boring summers, great junkyard, etc, etc). The voltage regulator wasn't as integrated on that cluster as it is on the normal 140 cluster - and I initially hooked up straight 12 volts to the gauges. But I immediately noticed the gauges pegging when I turned the key on for the first time, and spent a bit pondering a 140 wiring diagram before I found the voltage stabilizer between the gauges and the rest of the car. (Note - by that time the poor 122 also had the donor 142E's radiator, B20E engine, M41 trans, driveshaft, rear axle, gas tank, and front seats!)

The wiring diagram indicated that the heated contact is a bypass to send 12 volts through, and there is a second resistance path that drops the voltage down to some lower level. After the initial few seconds the bypass opens and remains open until the cars is switched off for a while and it cools back down. If it cycled it would tend to make the gauges go up and down - they react pretty quickly to 12 volts. Actually you could 'disaster proof' a voltage stabilizer by disabling the bypass circuit. That way it could never stick on and fry your gauges - but it would take 10 - 15 seconds for them to slowly come up to their proper readings when the key is turned on.