From what I have written down having compared sizes last year, the Aldi one is 41cm diameter. It's smaller than the mid-sized Smokey Mountain, and obviously smaller too than the 47cm weber kettle. My Kamado Joe Classic II is 46cm, and I will say I'm glad it's no smaller than it is. I've yet to try a full brisket on it, but I know that it'll barely fit. Need to 'mound up' and even then you won't manage a large packer
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On the aldi at 41cm you'll fit pork shoulders, lamb legs, whole chickens no problem, but you might not have a whole lot of room for much else to go on at the same time. Even moreso if you are setting up 2 zone cooking. On my KJ I can fit a large lamb shoulder and 5 jacket potatoes, or 2 racks of st louis cut ribs with a few corns on the cob, that sort of thing.
I would say if you're serious about this sort of cooking, you want something big enough (so if budget rules out a bigger kamado, look to a WSM or similar), and if you're not then you don't really need a kamado, so it does seem like a bit of a novelty to me. There again plenty of people are very satisfied with them, just throwing in my 2p.