Well.. Note that you don't have to let others handle your bitcoins. This means you don't risk of some service running away with your money. Top 3 risks I can think of right now with Joinmarket are these, not in any particular order:

1. Yield generators wallet must be kept on online machine, as the bot needs to (or may need to) access it frequently. You could of course have yourself between the bot and the wallet but I guess that's hardly worth for the 1% gains per year. Especially when coinjoiners will not accept too long delays from yield generators.

2. Code errors. There might be a bug which could cause coin loss. After all the program is interacting with the Internet and complete strangers in there.

3. Regulation. Some goverments could rule that running yield generator is illegal as it attempts to hide the traces of the money flow. One could use Tor or such, though.

You don't need to trust some 3rd party service and their wallet management here to gain that 1%. Using some margin etc. services may get you a lot better interest but holding gets you 0%.