I want to know if TRC 20 blockchain is safe to use?
It is secure, I have transferred USDT many times with the TRC20 network, I never got any problems. If it is not secure enough, the top exchange like Binance won't provide it as one of the options of the network for withdrawal or transfer coins. Just use TRC20 as long as it is free or cheap, I guess the fees will increase in the future along with more people use it.
some of the major exchanges do have USDT listed on the TRC20 network. and of course, some would have argued about the lower cost.
both of them are still safe for transactions. we just want to use which network is more convenient. with high costs but if we can afford it I think there is no problem.