As Mike pointed out, temp sticks are cheap and accurate. I would not buy a full set unless I had a specific need for all the temperature ranges. Instead I would purchase the tempsticks needed for the work at hand.

I have and use an infra red thermometer for informal use. It has been useful, especially for "clandestine" checks on preheat and portable rod ovens. The problem with it is that you will get different readings on clean, shiny surfaces as opposed to dull dark surfaces. In fact the instructions state that the most accurate results are on non-glossy black surfaces. Something to do with emissivity, which I won't even try to explain because I don't understand it at this time. What I do understand is that shiny surfaces that melted 500 deg F tempsticks might show only 300-400 deg with the infra red. You have to be careful and consistent to get accurate readings.

Also, temp sticks are accurate to 1% or 2% of their rating. You can even get certified temp sticks if you need them. Infra red thermometers can be calibrated, for a price, but then you still have to use them under controlled conditions to assure accuracy.

If you are an independent QA inspector, very often the contractor is required to provide the use of appropriate temp sticks.
And if an independent inspector uses infra red on a job I am doing QC on, I still want to verify the readings with tempsticks, based on my experiences.

Finally, I should mention that temp sticks do need to be stored properly. You don't want to get them wet. And I don't know how long a shelf life they have so on a "critical" job, I would make sure I used fresh ones.
Chet Guilford