The performances you hear, are professionals playing the instrument, and were recorded just after the Grand Piano had been launched in 1990.
The Grand Piano (which looked like a Mini Grand design) had a fully weighted hammer action type keyboard. The instrument contained 8 voices which included 2 Grand’s, 2 Stage, 2 Electrics and 2 Harpsichords, which were all contained in a 3Mb Rom Bank. It was based on the Livestyle sound system which Wersi had introduced in 1989. (The first with 24 bit processing and 64 note polyphony) As a comparison the current Wersi Giga Piano, has Grand Piano sample sizes of over 1 GB per voice and 256 note polyphony with 32 bit processing, and operates under the Wersi OAS system.
The Demo itself is in 2 parts, the first half was designed to show the piano in a live situation, and therefore features Real Bass and Drums for backing, the second half was produced to show how it could be combined with existing electronic instruments, in this case the Wersi Spectra Organ. (Which was released in the mid to late eighties, and featured 16 Bit processing with a 128Kb Rom bank, and a matching 128Kb Ram bank with 32 notes of polyphony)
The backings used for the second half were a combination of the Spectra Styles and its sequencer. (All the sounds (Except of course the Piano) were standard Spectra voices)
As to the availability and price of the Grand Piano, they do occasionally show up on eBay. (Mainly the German one)

Bill