I've eaten at Chisholm Trail BBQ several times. The BBQ is decent but nowhere near as good as Black's or Kreutz. They have a large selection of food, including chicken fajitas, but I recommend sticking with the BBQ. In my experiences, the service has not been friendly - certainly not the small town Texas charm you would expect. The drive through is convenient but slow.
Unless you're looking for a less expensive option, go with Blacks or Kreutz for the BBQ that Lockhart is famous for.