I've been asked about this in my tinnitus postbag on Quora today.
"Quietus" is marketed in the US as a homeopathic, anti-inflammatory, antioxidant. It contains:
Black cohosh
Motherwort
Kelp
Hops
L-thyrosine
Yam
Fenugreek
Dong Qai
Some of these ingredients are actively dangerous, linked to miscarriage, liver damage and thyroid damage. So just for starters, please don't take it due to these reasons. And please don't up your dose when it inevitably doesn't work.
Some people claim success such as "after 3 days my ears felt like they opened up, and my tinnitus got better". A head cold that has blocked your ears could be expected to relieve itself in this way, and yes once your ears unbung, your tinnitus is likely to be less noticeable as sound floods back in.
Many, many more simply report losing $100 to this stuff, and being very angry. I expect that is the most likely outcome, since if it is indeed in homeopathic quantities (i.e. nil) it's a very expensive product.
Theories of anti-inflammatory and anti-oxidant therapies are interesting, and if your tinnitus is new, recent or only happens when you have a cold, you may want to try an anti-inflammatory to see if it helps. But there are anti-inflammatory agents that cost pennies, not $100. This supplement is targeted at those in long-term distress, not those who get tinnitus for a few days when they have a cold.
I would like to think the people who made this genuinely believe it works, otherwise I despair about the state of the world and how people can leech off the misfortune of others. There is nothing in there apart from maybe hops that can help.
Hops are genuinely anxiety-relieving, and you can buy them on their own in decent doses for a few pounds. They may help you relax and drift off to sleep - read the dose and safety information before deciding to take them
Anti-oxidants exist, at a much cheaper price, that have been studied and are thought to be otoprotective (limited but promising evidence). N-Acetyl Cysteine is one such drug, which your body uses to make glutathione (an anti-oxidant, which mops up free radicals). This is not particularly necessary as a supplement, because it is found in many foods, but if you wanted to try a tablet which has potential to help your ears and prevent hearing loss/tinnitus from getting worse, I would use that one! Even so, I don't recommend it for tinnitus as it is highly unlikely to reverse your perception of the T signal.
I'm sorry to say that there is still no evidence - for Quietus or any other ingredient - that shows a clinically significant reduction in tinnitus perception. That's not to say that something will not come up in the future, we are learning more every day! But there is absolutely no good reason to spend your money on this one. If you have $100 to spare, treat yourself to a massage, or something else that you find relaxing. Relaxation and distraction is the best thing you can do for your tinnitus.