The investment advice is highly questionable, not based on facts, and seems to be written from a purely emotional state of mind.

He advises to pay off your mortgage, however, in the German Hyperinflation, farmers and holders of urban property benefited by having inflation wiping out their mortgage debt. However, property owners received no income, since rents were frozen by government intervention. After the stabilization, heavy new taxes and the urgent need for cash forced most holders to re-mortgage their property, often more heavily than originally, so that their gains were illusory. Still, those who held real estate throughout managed to save the capital thus invested. However, those who sold during the inflation (often through desperate need for cash) fared poorly. Because it brought no income, real estate sold at extremely low real price levels during inflation.

It makes absolutely no sense to use today’s dollars, which are more valuable than each subsequent dollar received in the future during the hyperinflation, to pay off debts with fixed interest rates today. The beauty of a hyperinflation is that you can pay fixed interest rate debt off to the lender with worthless currency. Almost all mortgages were completely paid off during the German hyperinflation.

He indicates that stock markets are terrible investments during periods of hyperinflation. If you study the German Hyperinflation, January 1918 through November 1923, one stock index share went from 126 to 23,680,000 million in nominal Reichsmarks. The German stock market provided one “release valve” for the pressures of hyperinflation.

However, if you measure the German stock market during this period in US Dollars (at that time backed in gold). The German stock market index was equivalent to $100 in 1913 and by January 1918 it had reached $101.55. In October 1922 was at $2.72 [sic], and in November, 1923 was $39.36. So the gain of 187,936 million times in Reichsmarks amounted to a 60% loss in US dollars."

So, during the initial stages of Hyperinflation (1913-1918; 5 years), investments in the stock market during a period of hyperinflation actually maintained their purchasing power.

From USA Gold, an article written about the German Hyperinflation in regards to using stocks as an inflation hedge:

In inflation, common stocks are generally considered a desirable hedge to protect against or even to profit from the rise in prices.
Getting down to specifics, we can say that those who bought a well-diversified list of stocks in solid, well-established companies quite early in the inflation and who held on throughout the period and also through the stabilization crisis saved much or all of their capital. However, there were many pitfalls along the wayside for the greedy, the fearful and the over-clever. Those who did best were investors with a certain unemotional, stolid character, a basic confidence that strong, well-managed companies would come through, and immunity to excitement, anxiety and speculative temptations.

He also advises that foreign markets (external to US bonds and stocks) will also crash. While the foreign markets may go up, or may go down, he is not factoring in that the foreign stock and bond markets are denominated in foreign currencies. If you have a good interest bearing foreign bond or a dividend paying stock, it will pay you income denominated in a currency other than US dollars. During the German Hyperinflation, those investors that had the foresight to exchange their Reichsmarks for other currencies maintained their purchasing power and holding a bond or a dividend paying stock denominated and paid in a foreign currency would do the same thing.

The only sound advice that he had was that bonds and cash denominated in US dollars are horrible investments and a sound portfolio should include gold and silver.