One of these days I want to get a second one and space them across the bottom. Until then, it's nice to see that big dial from 15 ft away and if the pointer is straight up I know I'm at 250 to 260 at the cook.I like the Tel Tru's as well. I have them on all my smokers.
Once you check the Tel Tru against a therm on the grate & see if there is any difference then you can make adjustments.
My Lang came with a Tel Tru on the end opposite of the firebox.
If I were building a smoker I would put 3 of them on the lid.
Left, middle, & right side.
Al