Any opinions? For example some authors talk about mercury.
In my opinion, yes, as long as you don’t over do it. This question might be good for the general questions forum.
The ‘canned’ part isn’t the danger with mercury. Mercury is bioaccumulative, meaning, generally, the larger the fish, the higher the likelihood of contamination. And the tuna species harvested for canning are large predatory fish.
Switch to sardines if you’re concerned.
Well, it’s dead. Might be a bit late to start thinking about the safety of the tuna.
If you’re concerned about mercury, get “chunk light” (the tan-pinkish stuff) instead of white or albacore tuna. As said, the latter tends to be a larger fish. Personally I don’t think it’s a big issue, but then I don’t eat tuna daily.
Sardines are gigantic! Go anchovy. Plus your breath will scare away danger.
Non-mercury, it’s fine to eat as long as the can isn’t bulging.
Lurking,
The can I have next to me says “solid light tuna” and “yellowfin”. How safe is that?
It amuses me when people ask if things that have no chance of ever hurting them are safe, when there are so many extremely dangerous (relatively) things they participate in daily without even thinking about it. Yes, tuna is safe. How do I know? The hundreds of millions of cans of it consumed over decades and the lack of overall deaths blamed on tuna. Hell, I’ve probably had in the thousands of cans in my lifetime, and somehow, I’m still here.
My cats say that tuna is perfectly safe to eat, as long as it’s canned and they are given the tuna juice. They say that the stuff in pouches without liquid is very, very dangerous for humans to eat.
My cats are my cite.
I’ve met cats like that. They are not to be trusted. 
Trust me, it IS dangerous to eat tuna around those cats if they are not given their due offering.
Invariably fatal.
For the tuna.
But hey, I heard someone consumed a canned food to excess and had some health problems, so they sued the company. Was it tuna?
Define “safe.”
The edge of the can top is very sharp.
In moderation it’s safe. I recall an extreme case where a man literally ate a can or more per day for years, and was eating a type that had abnormally high mercury levels. That caused acute mercury poisoning. So don’t do that.
Mercury is much more toxic to children. Therefore, children and pregnant women should be particularly careful about eating too much tuna. The EPA (conservatively) suggests that pregnant women consume no more than a can of tuna per week.
So for a healthy adult, you should have no reason to worry about consuming tuna two or three times per week. Even more than that ought to be fine, in most cases.
I love eating canned tuna at work. That way I don’t have to share with the kitties.
I was hoping for Dustin Hoffman and several dozen tins of diamonds…