For people with vacuum cleaners, is it worth it if you don't use carpets and there's just hard floor in your house?

definitely

100% yes

Yes ofcourse. Don't know your situation with kids - but our kids drop stuff on floors all the time -- having a handheld vacuum or cord-free vacuum makes it super convenient to just clean up. They definitely help with the carpets - but floors - definitely. Especially during the pandemic when we have had to be without help for many months. However, while we have used them mostly for floor & carpets and the occasional cleaning of the couches, anything else (like fans, etc) don't work well with them.