I agree it's a piece of crap, which is a shame because their other stuff is pretty nice. I have adjusted mine ad nauseum. It seems like maybe it's accurate in the mash temp range (the range I care about most), except that's not really true, either. It basically "sticks" around 150 when the temperature gets in that range. I have then subsequently raised the mash bed temp to 168F for a mash out, while continuously recirculating RIGHT OVER THE PROBE, and it still stays around 150.
I'll stick with my thermapen.
And, actually I keep meaning to put a plug in that hole instead of the Brewmometer so that pulling the bag out during a BIAB is a little easier.