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I used one many years ago. Unless you have a special use for them, like taking the temperature of plants like I did, they are not much help. They will take body surface temperature but not internal.
Surface body temp would be fine as it is an infection in my knee I am trying to keep track of but that was a secondary thought. The actual reason for getting one so that I could keep track of temps throughout the whole tank. I have strip thermometers in the bottom corners & my TDS meter for top tank temps but no way of telling if the water is a relatively uniform temp or if there are cold spots I should deal with.
I picked up one labelled for use as a grilling tool awhile ago for a couple bucks on clearance. It gets used almost exclusively to temp water coming out of the faucet for water changes. I haven't used it a lot for temping tanks, but I haven't fiddled with my heaters in quite awhile. The readings I was getting were pretty static all over the tanks so I don't monitor it closely