I recently bought 3 ThermoPop but haven't tried one out.
I usually use a ThermoPen from Wally World.
Brisket needs some fat to help cook the meat even if you drain it away when done.
Brisket isn't pot roast for a Sunday dinner cook. The taters will be mush long before the meat is cooked to tender.
I place the potatoes in 1.5 hours before slicing. Thats why I try to calculate when both will be ready at the same time