Bitcoin is the largest ponzi scheme. If there are no new investors, the price falls very deeply. Only the demand of greedy people raises the price. It consists of only speculation.
Xaurum is slightly different. The essence is gold and at the moment there is a gold cover of about 1000 XAUR for 1 g of gold. With new investors, gold is bought and in a few years, the gold cover will be 100 XAUR for 1 g of gold. The investor is not buying air but a certificate of ownership of gold. And this gold will be more from year to year.