I dove at Kuchundi, near Dar, a couple of years ago. The dive op was at the White Sands Hotel, and their equipment was excellent. If you want to dive away from crowds this is an excellent destination. My son and I did a number of dives as the only guests on the RIB. Fish life is abundant, and reefs generally healthy. The most obvious down side is that the locals regularly engage in dynamite fishing, which leaves loud bangs in your ears and patches of dead coral. It has also driven away most of the large fish and the dolphins...
HTH,
Victor J.