All bitUSD is fungible so it doesn't matter who issued the particular bitUSD you buy. The collateral requirement is enforced by the blockchain protocol, and the blockchain hosts an active exchange. If the value of any bitUSD issuer's the collateral drops below 175% of their bitUSD debt, the blockchain offers their collateral for sale on the exchange at up to a 10% discount from the current exchange rate to pay the debt. I like holding some bitAssets not so much for stability as so I can pick up cheap collateral off of margin calls after sudden drops. You can also 'force settle' your bitUSD and demand a dollar worth of BTS per bitUSD after a delay, which settles that amount of debt from the least collateralized issuer positions.
You can look at asset details on bitUSD here:
https://openledger.io/asset/USD
It's tragic how poorly marketed BitShares and its market pegged assets have been. It's a brilliant system for stability without counterparty risk, but most people who even know about it just think it's like Tether.
Thanks for explaining! I guess to understand these dynamics, it would need much more knowledge over how this market works and who takes the time, to research and understand it properly? The simple reason why people just think it´s like Tether is simply, because at the first look it looks like it - they would need some kind of easy video explanation to make people figure out the differences....