There are MANY variants of the FE-5680, most of which are poorly documented (proprietary). The most desirable are the 1-20 MHz programmable ones. The most common are the fixed 10 MHz sinewave output. Most but not all of these have the 1PPS output, as well. Some units are only 1PPS, some output unusual frequencies for specific applications. There are also variants with or without separate SMA RF output jacks, and units that only need the +15 power, with the +5V supply developed internally.
Some people have come across units that need 24V or 48V power, as well as units with an analog C-field trim input (and no serial communications option).