I cook briskets in my MES all the time. I normally split a packer brisket into flat and point chunks, then cook each to the appropriate temp. I use either pecan or oak chips, and smoke for most of the cook. I cook at 225 until the meat temperature is 200-205, then wrap and rest in an ice chest. The flat is frequently done before the point. Depending on the brisket it may take 16-20 hours to get to temp (and tender).
This, and yes, an MES will take FOREVER to get to 200. Stick with it.