Is a great addition so it would get 5 stars, but one gripe is that the KBJ charcoal basket doesn't fit into the KBJ II so that the diffuser plates can sit flat and snugly on top due to the hooks it comes with. The hooks aim to hang off the flexible cooking rack to enable the ash basket to be easily lifted out with it, however with the charcoal basket resting on the ceramic firebox the hooks of the basket then stick out above where they should. The hooks sticking out stop the diffuser plates sitting flat. I have seen people then laying the diffuser plates on top of the KJ accessory rack but that's not what its meant for nor what I want as I need that for a drip tray to sit above the diffuser and below the grill rack. Reading other review threads it seems people saw off the hooks or mod them somehow. OK you have to accept it may then be harder/messier to get it so gets a minus on that. I'm going to see what I can do to mod first (bend the hooks to be lower) before hacksaw as last resort.
Note: this is likely also so for the KJ II as well as KBJ II (which I have) - it may not be the case for the KJ III / KBJ III as they are deeper.