I have a couple the Meater+ for just temp and the BGE temp probe with fan control. What always amazes me on LONG cooks is the initial divergence of the temps from the two devices in the early stages. As the cook progress, usually 2 to 4 hours in, the temps do a better job of converging, never exactly the same, but close.
One thing I just read (learned) that years of experience confirm but never really clicked, is that on long cooks or even the shorter ones with higher heats, the metal probe will conduct heat into the meat and change the temp at/near the probe. This results in a higher than actual temperature than is present throughout the meat. I will be a little more careful to use an instant read to confirm total temp distribution in the future!
Gig'em, Ole Army Class of '70