Even if you could find legit mixer (doesn't steal your USDT), i have to remind you that,
1. Tether have capability to freeze USDT. Example, https://en.ethereumworldnews.com/bitfinex-and-tether-freeze-33m-usdt-from-kucoin-hack/
2. Some people argue that TRON isn't really decentralized due to low number of Super Representative.
I hope Tether doesn't have plan to freeze mixed USDT.
I think it's a great possibility. I would expect USDT to be frozen at any time especially if i hold large amount of it. USDT remains to be one of the most dangerous currency [worst than fiat].