It certainly looks correct to me (though I am not a native speaker). I have always thought of the amba- relative and the relative "infix" as being equivalent, except there are some places the "infix" does not work, such as with conditional tenses: Mtu ambaye ukimwona utacheka; mtu ambaye (kama) ungemwona ungecheka; mtu ambaye (kama) ungalimwona, ungalicheka. And sometimes the amba- relative helps to clarify complicated sentences. And there probably other cases that don't come to mind at the moment where the amba- relative is required or preferred.

I thought you needed the object infix.

You can say "Kitabu ninachopenda ni hiki" without using the object infix, but "Kitabu ninapenda ni hiki" is wrong. You have to use the relative infix or an "amba" construction: "Kitabu ambacho ninapenda ni hiki.