Front end interface of Mil-std 1553 IP cores are suitable where CPU is not present/required, short messages are to be sent over the bus etc. This type of mil-std-1553 IP cores are easy to integrate in designs as there is no need of any software and the data is read or written based on word count or 1553 sub address.
Legacy interface of Mil-std-1553 IP cores are apt for any implementation and incorporate a backend logic that can arrange messages in predefined memory which simplifies the interface between a 1553 bus and local CPU.
The Extended reliability Mil-std-1553 IP cores are suitable for high reliability implementations like space applications. This type of Mil-std-1553 IP cores are already being used by NASA to overcome problems like radiation.