This Thomann bag fits the Allen & Heath CQ12T mixer perfectly. It has a couple of velcro straps inside to secure the mixer in transit, without being too snug. There's enough room in the front pocket to fit the PSU and mains lead, plus perhaps one or two further leads if required.
The bag is made from a good quality material which feels robust enough to withstand regular gigging. It also has a shoulder strap, which I always like to see, as it cuts down on the number of trips made to and from the car at gigs! I also think it's well-priced.