Translation:These are modern and efficient bicycles.
ezek a modern biciklik = these modern bikes (or: these are the modern bikes)
I think I know what he meant! "Ezek a modern biciklik!" by itself is an exclamation. You would use it to describe a sense of wonder or surprise or even anger, but that's where the sentence ends. For example some guys on modern bikes race past you, then you would say it as such!
I think I figured this out. The version I actually had in mind was "Ezek a biciklik modern es hatekony". But this is different, because "Ezek a" is followed by "biciklik". In our example this is not the case, so we need a standalone version of this demonstrative pronoun, which is "Ezek".