I think having an infrared is somewhat useful and can be informative. You know better what's going on at the grate level and can spot unevenness that might indicate a problem. My main thought is that Thermoworks makes professional grade products and has to price them accordingly. For backyard bbqers using it only occasionally, I think the Thermoworks unit, even with the very nice discount, might be overkill. Not at all am I saying that someone who can afford it shouldn't buy one. Just that the degree of accuracy/speed, etc. for this application doesn't seem to me to be nearly as critical as it is for testing your food.
My 15 buck Harbor Freight one is actually a pretty nice basic unit. (The one HF offers now looks to be even better. See add above.) At that price, it might make more sense to someone who otherwise wouldn't jump in to buy a professional grade infrared.
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Broilmaster grills can get HOT!