Nope, mule accounts aren't worth it.
I prefer storing 8 bil gold on my botting accounts, feels way safer.
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As for the mule - if you don't bot on it it shouldn't ever get banned, doesn't matter what you do with it they can't prove you did anything wrong and the mule itself doesn't go over any rules.
So yes i use a mule same ip and same time as my other bots run, i play it legit and it can't be banned due to nothing it does is wrong.
For the same reason they can ban you for trading with another player (items for gold or getting stuff for free from someone) due to him being a botter - doesn't mean you know this and doesn't mean it matters at all.