I went with 15 family members on the Parranda. (Guilty as Charged)
We loved it. The Parranda recently burned and sank, so we booked a return on the MS Grace. It mysteriously became "unavailable" only three weeks before our trip. We went on safari in South Africa instead. Geo Expeditions arranged both trips. They are superb.

Chartering a small yacht for just your group plus a naturalist or two is the only way to go, if you're a group who enjoys one another. Hard to beat a trip like this. (Except maybe an African safari!)