Yeah. In theory they are broken. But in practice they can work for a while. They work by taking a collateral and splitting in two. The first part has some fix

Yeah. In theory they are broken. But in practice they can work for a while. They work by taking a collateral and splitting in two. The first part has some fixed value in an external currency. The other part is the rest. And that works as long as the rest has some value. However here we are talking about programming errors in the implementation. And Solidity/Ethereum is really at fault. How do you implement a contract in Ethereum where a certain thing happens the price of Ethereum drops below XXXX dollars? You can (as this is what MakerDAO and others are doing) only it is silly complex to do. It really should not be.