I have stopped using Bitfinex due to this article and wary of using Bittrex which also uses USDT, although USDT is more compliant with US laws. If USDT is busted can Bittrex come out and say .. sorry there is no money ..
Sad that I got scared of using Bitfinex though .. it is the best platform for day to day trading.
I've shared the same concerns about the Tether supply. It's increased more than 6x since Bitfinex (and Tether) lost its banking capabilities. But this can possibly be explained if the hundreds of millions of USDT represents an exodus of funds from Bitfinex to exchanges that accept USDT for deposit, like Poloniex, Bittrex or Kraken.
Even aside from the worry that they are being printed, they are tied to Bitfinex (hence third party risk), and frankly, I think Bitfinex is facing a legal shitstorm in the future, for being an unlicensed MSB and for their whole token distribution scheme. If anything happens to Bitfinex, the value of USDT could plummet, and since it is a standalone asset (not USD obligations of another exchange), customers on many exchanges could be devastated as a result.
I also like their interface and trading options a lot, but they come with a lot of baggage. On top of it, they are a security risk, given that they still can't even explain how they got hacked last year.