Perhaps the opitimum is a fixed elt with a crash switch, that can be unclipped from the airframe and carried off by you.
IMO, optimum is a fixed ELT and a separate PLB (attached to pilot's life vest if over water). For routine over water ops, a PLB fpr each pax is recommended by some. The problem with a fixed ELT is that it may become inaccessible following a crash.
None of the units that I operate with have 243.0 any more, but all have 406/121.5,
The Artex C406 series, which is widely used in helicopters, transmits on 121, 243, and 406. Some other models/brands have dropped the 243 freq.