They don't guarantee you zero downside compared to investing in the index, though, but compared to putting your money under the mattress. It's relatively easy

They don't guarantee you zero downside compared to investing in the index, though, but compared to putting your money under the mattress. It's relatively easy to achieve a return profile like these promise with some combination of Treasuries and index options (at least while Treasuries pay 5%!), and the ETFs are doing this kind of financial engineering rather than promising to beat the market through stock-picking skill.