The findstr command ignores piped input in ReactOS 0.4.10. As a consequence command sequences like this one do not work:
C:\> systeminfo | findstr /C:"OS Version"
Instead of returning any lines containing the string "OS Version" to stdout as it should, the findstr command exhibits the default behavior of returning help text and exiting.
As an aside, several documented switches are not (yet) implemented, see the findstr command reference for details: https://ss64.com/nt/findstr.html. In fact, judging by the output it looks like the findstr command is currently just an alias for for the find command in the 0.4.10 build of ReactOS.