I have one thing to add/suggestion for a change in the article:
From the list of daily holdings, it appears these funds are actually using a total return swap to achieve their leveraged positions by swapping the equity index return for some other rate of return. For example, the Ultra S&P 500 lists as of 5/14 $1,010,420,882.49 notional value in S&P 500 swap contracts.
Leveraged Market Cap ETFs [View article]
From the list of daily holdings, it appears these funds are actually using a total return swap to achieve their leveraged positions by swapping the equity index return for some other rate of return. For example, the Ultra S&P 500 lists as of 5/14 $1,010,420,882.49 notional value in S&P 500 swap contracts.