Gosh, it depends. If you lay each of them side by side you can probably tell if they are all the same engine. If they all have the same attachments then they are probably all Ryobi.
Good brand, but can't touch a Stihl. HD, Menards or Sears can't touch the service that a dealer can offer too. If you are not mechanically inclined, you should use a dealer and not the big box store. Northern qualifies as a small box store with lousy customer service.