While I'm sure that everyone on HN understands the seroconversion window period, this is simply not the case in the larger community. Ignorance about HIV is widespread. I cannot even begin to count the number of people who believe that pulling out before ejaculating affords some sort of magical protection from the virus. These are the same people who upon seeing a negative result would assume that they're safe without condoms.
The CDC states that the window period for detectable HIV antibody formation is three months; however, this figure is based on first generation HIV tests and is considered somewhat conservative. Public health experts like H. Hunter Handsfield state that detectable antibodies usually form in four to six weeks.
Whatever figure you choose to believe, it's a pretty significant time period. And it's a deadly one. It's during the window period that an HIV infected person is most infectious. Their viral loads are off the chart and they can unknowingly infect multiple people in a short period of time.
The "cure" for HIV is the same as it has always been: education and safer sex practices. HIV is largely a preventable disease. I would be okay with personal test kits if they were bundled with extremely clear educational packets printed in multiple languages. But this particular kit is advertised too much like a silver bullet to assure me that the manufacturers are anywhere near that responsible.