Since they never had a real audit i do not think it is safe and would stay clear from it as much as possible.
Is there an institution that deserves to audit
tether.to? I don't know if any institution has the right to audit a crypto project. By the way, even a project is audited, I am not sure the team will publish the detail to the public. You must contact the team privately if you are really curious about the audit. FYI, for me, as long as it is one of the top crypto coins, it will be quite safe although no audit announcement on the site.
That is a big problem in my opinion. A product like Tether and the company behind it should be obliged to frequently provide a full audit report about the reserves that are supposed to back USDT 1 to 1. We are not talking about a stable currency that is handling a few million USD volume per day. We are talking about a massive product/market that could cause enormous harm to the whole industry if something goes wrong or if mistrust arises. I have no idea whether there is really a dollar for every single Tether.