The rapid self-test "Flowflex" by ACON Biotech with the white packaging (see my photo) of 25 tests is incredibly reliable. It can detect even the lowest viral load (it produces a faint line or multiple faint lines on the test, depending on the viral load) and has been approved by the FDA of the USA.
However, be careful with the blue packaging (labeled as self-testing) of 25, 5, and 1 tests, as they have been deemed unreliable by the FDA of the USA, as they give many false positive or negative results.
Let me describe my positive experience with the tests from the white packaging that I conducted on my wife and daughter who contracted COVID-19.
My daughter developed a fever on June 24th, and I tested her: positive. I went to a diagnostic center in my area on Saturday, and the result was negative (note: not a pharmacy, as when I needed to take a test to attend a hospital session, they gave me the swab stick to collect the sample myself). I thought, it can't be that my wife tests positive on the self-test and it is confirmed by the rapid test, while the test on my daughter on Friday is positive and the rapid test is negative. So, I went to another diagnostic center for a rapid test, and of course, my daughter tested positive.
So, be careful with the tests and how you conduct them. The samples collected should be rhinopharyngeal and not nasal if you want reliable results.
Then, on Tuesday, my wife went to a diagnostic center (at home, I had tested her positive), to take a test to get a certificate for her work. The result? Negative. She went to a team from EODY (National Public Health Organization in Greece), who don't joke around, they take rhinopharyngeal samples. The result? Still positive for my wife (I knew it because these self-tests are incredibly reliable).
On July 1st, my daughter's test started to show a fainter line, on Saturday it was even fainter, on Sunday even fainter, and even today, Monday (11th day since she tested positive), it is very faint, you need good observation to see it. So, these tests are so sensitive that they can detect even the tiniest presence of the virus.
Recommendation...!!!! To have accurate results (not only with these tests but with all tests from all manufacturers) and to be at ease with yourself and those around you, the samples you take should be rhinopharyngeal. This way, you catch the virus at the beginning, and also, you know when the virus has been cleared from your body.
That's why we always take rhinopharyngeal samples... not nasal ones..!!!!