Lid thermos are not notoriously wrong, you are getting the temp that is at the top of the lid which is going to be hotter than at the food grate. If you know this difference then you know what to shoot for with the lid thermo.
Dropping a remote thermo in the lid is ok if you don't have to add charcoal or rotate the meat. Lid thermo and an instant read thermo is the minimum you need. After cooking the same protein for the third time you know when you're getting close to done.
Case in point this past thanksgiving turkey was the first time I butterflied a turkey. Using weber charcoal holders in a 22" made things very tight, every thirty mins I added charcoal and rotated the bird to prevent burning. Now if I had a remote thermo in the turkey or thru the lid that presents more problems to deal with. After 2 1/2 hrs I started checking with the instant read, the turkey came out pretty good.
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