@NYARAIH-BANDA when mapping SN Multicast to Multi-cast MAC address, is it not that the last 24 bits of the unicast are appended to 33-33-FF?

Absolutely. And the efficiency is network-wide because there will be no broadcast ARP messages as is the case in IPv4 that need to be processed and discarded.

So the solicited-node multicast address prefix is always ff02::1:ff00:0/104

The last 24 bits would be picked from the global unicast interface address of an interface of the link-local address if that is not available.