Bouzoukis 01
The bouzouki was picked up by irish musicians travelling abroad and adapted for their use by retuning to GDAE. Modern makers then started producing them with flat backs which made them almost identical to the octave mandola.
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The crucial difference is the scale length, which is longer. This can affect fingering, but also affects sound because the strings are thinner. Generally the mandolas are better at tunes, bouzoukis for accompanying, but this is not a strict rule.