I am super late to the party here but thought my contributions to the post could still be of benefit to the OP (or anyone else doing some research on the topic).
I dived in Mozambique in January 2023 based out of both Tofo (various local sites) and Vilanculos (going to the Bazaruto National Marine Park). It is purely my one anecdotal experience but I was overall very underwhelmed with my diving experiences there and am a big megafauna fan. To be fair, I am also hugely spoiled, having dived in various places around the globe where the megafauna is out of this world (mostly sites in the Pacific).
Out of Tofo, visibility was at times murky but we did encounter a number of whale sharks feeding on plankton on the surface - however this was only surface snorkeling between dives - I did not encounter any while we were actually diving on the various sites. I was not a fan of this however as there were so many boats (mix of those specifically snorkelling for whale sharks and dive boats) and it felt a bit overwhelming for the animals to be chased and have so many people jumping in on top of and around them. The encounters were thus rather fleeting. We also caught some reef mantas buzzing along but they were quickly chased away. Again, never saw them while on an actual dive.
Otherwise, I found the sites to be a bit boring - a bit of reef life but not worth a trip around the world to see IMO.
Tofo, otherwise, was a cute enough little tourist town with nice beach to walk up and down (I did take garbage bags out on my walks to clean up all the garbage as I went) and a few nice restaurants (though I did feel immensely uncomfortable with the waiters at various times asking me for money - aside from what I owed in bill and tip - and the sexual harassment). I did not feel unsafe however.
Where I did feel unsafe was Vilanculos town (street harassment was rather direct and hostile) though the beach there is quite beautiful. I did a number of dives into Bazaruto - the islands and sand dunes are very pretty and nice during a surface interval but the dives weren't all that exciting - no megafauna really. Some coral, reef fish, the occasional reef shark, turtle, octopus. Still pretty lovely but nothing that was worth the long trip from Europe for me. I have heard the megafauna may be better (in all seasons) further south in Eastern South Africa (Aliwal Shoal, Protea Banks) but have not been personally to attest to this.
