Telltru calibration - how often?

[Hockeydudde]

I accidentally ordered the telltru's for my new smoker that don't allow calibration adjustment.
If anyone has the adjustable ones, how often do you adjust and how much do they drift over time?
Is it worth sending these back and offering the adjustable ones?

Edited to add: if they will eventually be off by 15 deg, I don't care. If it'll be closer to 50 or more, I want the adjustable ones.
Thanks!

 

[kelbro]

Mine have never moved to +/- 5° of my digitals.

 

[smokebuzz]

I typically check mine once or twice a year, never off enough to want to adjust.

 

[Hockeydudde]

Thanks @kelbro and @smokebuzz .
Good enough for me, I'll keep these ones, not worth the hassle.