I don't have a Kuuma, but do have an ash pan (box?). I take most of the ash out of my boiler with a scoop. But what does end up in the ash pan, I take that out with a scoop too when it needs it. It never gets completely clean-like empty that way - I just scoop out what I easily can & leave the rest there for the next time when I'm not getting half decently full scoops anymore.Well, if it's open ended, the stuff that falls down while the pan is removed doesn't get packed between the pan and the back of the stove when you put the pan back in. So, I guess that would be one small advantage. Though the main reason I'm eyeing mine with a cutoff in mind, is, the open ended pan is a lot easier to tip the ashes into a 5 gal bucket without setting loose a cloud of ash dust. Having the ashes gently slide out of the pan seems better than having to turn the pan over and drop them.
I've only been burning this thing a couple of weeks, so maybe there's an obvious solution that hasn't become obvious to me yet. If so, somebody please enlighten me!