It will eventually fail too. When ETH collapses they won't be able to hold the stability for long.
I was skeptical of Maker at first, and they are backed by ETH, but they've stayed within 1% of their target price while ETH dropped 94%, so it seems to be working pretty well so far. They're working on a multi-collateral version.
I'm not sure which charts you are following, but as recently as yesterday they were 5% off target: https://coinmarketcap.com/currencies/dai/#charts
I don't think you can call DAI purely algorithmic because it needs oracles to work.
- Ones backed by fiat, or allegedly backed by fiat[0].
- Ones backed by commodities, e.g. the organisation that issues the UK's coinage (The Royal Mint) was looking at issuing RMG tokens backed by their gold reserves[1] (they've since stopped work on this even though it is still listed on their web site).
- Ones backed by other crypto assets, e.g. Maker DAO's DAI depends on ETH as its collateral.
- Ones not backed by any external asset outside of its own system, e.g. Basis.
The algorithms for the last class are particularly interesting in that they essentially have to model what a central bank does. I'd be interested to find out why Basis has failed. Is it just that they were unable to comply with US regulations? Or is it that the algorithm itself wasn't viable?
Point is that DAI has economic incentives in code to keep its price in check.
People who want to invest/speculate in cryptocurrency will often want some proportion of their portfolio value to be as stable as USD. But, actually holding true USD at exchanges/banks could be more complicated, requiring interfacing with legacy banking systems & regulations. A stablecoin allows USD value to be handled at exchanges (and transferred) in manners almost wholly analogous to other cryptocurrencies.
This simplifies, eg, a dApp hiring staff: you hire them for stable coins, which they cash out at various certified brokers.
Many exchanges, especially those that offer any type of contracts trading, are not under normal financial regulation and to the extent they even offer fiat denominated orderbooks there is a risk premium attached to it. When withdrawals are not guaranteed by by any type of regulatory body people could just as well trade pretend-dollars, and that's basically what stablecoins are.
Be cautious out there. At least these holders got their money back.
1. A base "asset" to hold with nearly instant ability to move, ideally without changing value relative to the reporting currency.
2. Moving assets around between exchanges/markets/wallets outside banking hours (9a-5p M-F).
3. Banking one-self (no intermediary ever required), the owner can determine the appropriate security procedures for their assets (granted this may well be not on target of the use-case...)