A brisket will come out pretty good at almost any temp on the Traeger. The key is to start checking for doneness when the internal temp hits about 180 (It probably won't be done at 180 but it's a good temp to start checking). Using the blunt object method. Poke it with a blunt object about 1/4"Ø, you should feel some resistance at 1st. Once you get past that innitial resistance, the blunt object should go in like a warm knife into butter. If you have time you can pull the brisket off a bit early, wrap it up in foil with some apple juice (or your liquid of choice) and put it in the cooler for an hour or 3.
When I got my 1st Traeger I used to do briskets and butts with the unit set @ 180°. I think it took about 14 hrs or so, but my memory is not what it used to be. Now I set it @ 225 (which is really closer to 250 on my 070's) they usually go about 8 hours in the cooker then into the cooler for a couple.