ERC20 detucts a lot of fee but TRC 20 on tron network, the transaction is free of cost.
I want to know if TRC 20 blockchain is safe to use and we can store our USDT there for long term ?
No need to store your USDT there for long term just for transaction cost. It is safe to transfer your USDT to TRC 20 (Tron) blockchain. The cost of TRC-20 USDT transaction is very low and can be withdrawn completely free from some exchanges like Binance, Kucoin etc. I often withdraw my asset by converting it to TRC-20 USDT.