On the standard 406 units for an aircraft, there are two types- one that has a gps or uses the plane's gps, and one that doesn't use GPS. The GPS units typically cost a touch more, but have the advantages of broadcasting to the COPASS/SARSAT folks your exact location, as determined by the GPS. The non-GPS units use signal triangulation from the satellites, which is not as accurate. Each pass of the satellite narrows it down. The non-GPS 406 units are still quite good and allow your position to be determined 100(?) times better than the old 121.5.
The search area for a 121.5 ELT is the size of the Washington, D.C., beltway. The search area for a 406 ELT that is not linked to GPS is that of a few city blocks, and one that is linked to GPS is akin to searching an area the size of a football field.