To directly answer you, yes there is no sustain pedal possible on the Pianet. Also, little to no dynamics are possible as the volume and tone are solely determined by the stickiness of the pad, which can't be controlled by how hard you play it.
As far as muddy, my Combo Pianet wasn't muddy at all. It had a brighter tone than a Wurlitzer. It sounded exactly like the one in These Eyes. There were earlier models of Pianet that had different reeds and were plucked by a rubber plectrum I believe that had a lot darker tone. Walrus would have had one of these earlier ones.