Oregano oil, in my opinion, should not be used or only with great caution. DEFINITELY not regularly. The new age health magazines probably do not mention that it contains volatile organic compounds (VOCs) that are toxic. One of these is thujone, a potent neurotoxin. Thujone is toxic to any living cell, particularly those in the liver, kidneys, and brain.
It is probably unlikely that a typical user would experience any lasting ill effects of the oil, but each bottle has an unknown amount of the harmful substances, and most likely no warnings to guide its use. From my research on thujone, I would guess that an amount of oregano oil that could have a true desired effect in vivo (e.g., antiviral, antifungal, antibacterial, anti-parasitic, etc.) would also have an unacceptably large undesired effect (e.g., liver damage). In other words, the safety-effectiveness ratio is not that good.
If you want to see if oregano oil has a desired effect for you, say antiviral, as good as is claimed, do an experiment on yourself by taking it when you have a viral infection, like a cold. I had many colds in my childhood and teens, and symptoms always lasted the standard 7-10 days no matter what I took. If I took oregano oil at the first sign of a cold and was symptom-free after 3 or 4 days, I'd be willing to use oregano oil temporarily as a cure for the cold virus. But I still wouldn't be surprised if it didn't work for a second cold; the first result could have been the placebo effect, or a short-lived flu rather than a cold, or an exceptionally potent batch of the oil, etc.
And I wouldn't use it long-term because 1) at any given time, I don't know the amount of harmful volatile organic compounds in a bottle of the oil, and 2) at any given moment, I don't know how good my liver is at detoxifying those compounds. I particularly don't know how #2 changes over time with exposure to #1.
In general, I would never personally orally ingest essential oils, period. I avoid using them topically as well; for example, I avoid sunscreens or other topical products that have long lists of essential oils in the ingredients. Many are irritating to skin.
There are many supplements with proven safety and health benefits, so I would focus my supplement budget on them.
Hope this helps.