After 30 years of casting, I use infrared.
Having cast lead bullets since the late 1970's (I think it was 1977) I now use the infrared exclusively, but I don't make any adjustments suggested by brickeye, even though he's absolutely correct and credit goes to his knowledge.
I cast bullets the best in the low 600's, but anywhere from 580 to 675 degrees F is excellent. Most of the time it stays where I set the controls, usually about 625. At that range of temps, the infrared is certainly close enough without adjustments. I only check when I add more lead, to make sure the temperature gets up near 600 to begin pouring again.
The infrared is also HIGHLY useful for mold temp. I cast the best when the aluminum mold is in the low 500's, the cast iron mold in the mid 500's, and the brass mold (yes, I still have old brass molds!) just at 500. Once again there is a wide range where it works great, anywhere from 500 to 550 d F for all three.
At those ranges, the infrared is handy for both the pot and the mold and surely accurate enough. But you select the tools that work the best for you. It's your hobby, go have fun your own way.