The keybed uses metal contact and provides a very good tactile feedback; moreover, the S2 and S3 features one of the best polyphonic aftertouch on the market, making them as excellent master keyboards. And as more notable features:
keyboard release velocity
four high-quality Analog Devices DACs on their audio chain
no portamento effect
double MIDI port sets (2 MIDI IN, 2 MIDI THRU, 2 MIDI OUT, separately configured)
S3 is 76-key, S2 is 61-key
The internal NiCd battery is prone to acid leakage and motherboard damage. I highly recommend to owners to replace the NiCd one with a NiMH battery, setting it aside from the motherboard and connected with a pair of wires, to avoid possible damage. It could be easily made without removing the motherboard, by simply cutting original battery leads and using them as terminals.
They are built like a tank, quite heavy compared with current keyboard production. The button keys on panel are, lilke as the traditional italian instruments, tiny and with small action range. The encoder could need some cleaning, but it restores to the original precision. Pitch and mod wheels are big and gives great feedback. The display is highly readable even in sunlight.