Windows has released its latest software windows 10 just after release of windows 8. therefore I think they may have not added new features apart from windows 8. Its just like the same version of windows. May be some security features are added to it but I don’t think it is enough to buy new version of it.
Besides from this some users don’t like the user interface as that of windows 8. moreover the computers are bit costly if it was preloaded with windows10. therefore I would not recommend to upgrade to windows 10