The Expert Sleepers ES-5 is a Gate/Clock/Sync expansion module for the ES-3 (from version Mk2 on). The connectors of the mk3 version are equipped with multicolor background lightning.
The ES-5 piggybacks on one of the ES-3's stereo channels to provide eight gate/clock/sync/MIDI outputs on the ES-5 itself. Furthermore you have further expansion headers to connect up to five ES-4 gate expanders. This means you can add 48 digital outputs to the ES-3!
The ES-5 is intended to be used with the latter versions of the ES-3 (Mk2, Mk3 and Mk4) as the first version has no expansions headers which means you would have to solder.