I don't think there is a good way to accurately quantify them. I prefer stable coins that are managed and regulated by US companies (like Gemini) and avoid ones with algorithmic stabilization.
I agree they're a little bit safer than unregulated or so called "algorithmic stablecoins". But they're still commercial-grade debt, not bank deposits or money market funds. You may as well invest into junk bonds.
Their ERC20 contracts are backdoor-ed, so the issuer may in some cases will be able to recover stolen funds, but I'm not sure it will help if the issues itself will go bankrupt, and pure-play Crypto companies like Gemini or Circle are high risk of going under, for example in case of crypto crash or regulatory change.