ReactOS is nice in theory only. They have a tendency to change their targets before meeting their goals, and are forever behind the curve and unstable. With better organization behind them and a larger community, they may one day make a viable alternative, but Linux or Mac are a much better alternative to Windows than ReatOS in its current state. I'm not advocating either as a replacement, and I do have my biases for Linux, but I also know that everyone has different needs for their use case, so without knowing what you need specifically, I can not make a suggestion. In any case, if you really need to use Windows for your needs, be thankful that the corporate overlords at Microsoft are still allowing you to disable S-Mode. Not sure how much longer that will last.