It works OK for me, but you have to be careful. The ST-E2 is infrared and needs a clear line of sight to the sensor on the flash unit. If you face the flash forward into the box you are blocking it. The bracket that comes with this is adjustable. This allows you to spin the head around on the flash and aim it into the box while pointing the front of the body where the sensor is towards the camera position. As long as you are mindful of this and make sure that the flash stays within the light cone of the ST-E2 it will work fine.....and so should the 24x24.
Thank you for your quick answer. I have just started using my flash off-camera and thought I might have wasted my money.