Never used a pellet cooker, I have use a gasser. There is a big difference between a commercial gasser and a residential gasser. Personally, I think you are putting way to much emphasis on the cooker still, you can make a great brisket on any cooker.
I poke at the meat and fuss with it, but, if I was going to use a thermometer, I would start checking at 185F. I used to start checking at 165F, which it will NEVER be done at, but, I was trying to learn the feel of the meat at each stage of the cook. I am pretty confident that I can read a brisket by feel now, but, the probe is a good backup. probe at 185F, and then every 45 minutes until if gets close. Then every thirty minutes until it is done. That small window of done is actually pretty easy to get close after a few tries.
me: I don't drink anymore
Yelonutz: me either, but, then again, I don't drink any less