I have a kit from 25 years ago.....K and L or something like that. I have every size from 2-12 and lots of plastic wire to make almost anything. The needles screw into the wire. I also still use the DPN's for socks and hats.
I like the kit over the straight needles as it packs smaller for when I'm traveling. I haven't seen any of the new kits but it was a good investment for me. I haven't bought any needles in a long long long time