The seller titled this as, "Rare - highly sought after." Hyperbole. These actually don't come up for sale too often but they can hardly be classified as "Rare." I have no data and will make no comments regarding potential demand.
If you hunt around the internet there are several interesting tales about these blowing up, so buyer beware. Regardless, I always wanted to check one of these out for fun, especially given lineage of its sister...
for those with cash burning a hole in their pockets, a Sansui AU-X1 Integrated Amp is currently listed on ebay for $1,250 "buy it now price"