I am not trying to kill the temp gun craze - but on singles - I can't find any need - as noted tho -- a cold side on a twin can be easily detected.
Frankly the so called ducting -or lets say the positioning of the twin cylinders in many cowls - is horrible - from an air flow standpoint
Typically the rear cyl is very close to a bulkhead.
I pylon mount my twins - so that there is a big distance from cylinders to bulkheads .
Where required - I redo the front of the model .
I know that the point and measure devices are handy - but for our uses - I sure wouldn't spend any money on one -