open loop is only referenced to when the engine is cold or cool, once at NOT (normal operating temp) the ECU will go into closed loop and start to refer the O2 sensor or trim pot.
by changing the value of the IAT input the ECU does not massively go fuel crazy, infact it more has an effect on ignition timing. The major factors that change fuelling are
1 rpm
2 baromatic pressure or absolute pressure (MAP - speed density based engine)
3 air mass (MAF engines) - MAF engines can account for BARO changes on the fly.
I have seen such devices and honestly they dont work, no test has ever been done by a certified resource that can prove their work, it falls into the same category of
Plugs
wires
conical air filters
fan shaped devices to stick into the air pipe
that you see at "burger bacha speed shops" of Pakistan.