I don't normally do BBQ's but somebody once told me that the rectangular BBQ's are best so that you can have a hot area at one end and a cooler area at the other. I would imagine a bucket BBQ has a uniform heat throughout which means you can't keep the finished items warm while cooking the rest.
IMHO, it is still possible to have "zones" with a bucket BBQ. Put the coal in the centre, and the outer edge will be cooler.
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