The Yamaha expander offers the following –

240 different sounds for right hand section, 240 sounds for chords and 240 sounds for bass.  2 jack plugs out of expander for stereo if required, midi signal in from accordion, midi through to enable more than one expander to be used at once, and midi out.  Memory on /off switch. 

Orange LCD back lit panel to show settings plus a number of buttons.  The buttons allow various channel selection and instrument selection settings.  Inspite of all these settings the unit is quite compact 11 inches deep, 8.5 inches wide by 2 inches tall.