Can this use the same SSID as my existing router?
So i won't have to change networks on devices when the signal gets weak as I move away from the main router.
Short answer No. I don't believe that any extender offers that feature. The extender acts as and creates its own network with its own password. I think you could name it the same or similar to your existing SSID, and have the same password. But even if you do that, the network will still show up as its own network in your wifi settings, because it is its own network. In my experience, my devices seem to connect to the closer/better signal as I move throughout my house. I believe there is a specific setting for that on android devices that will always search for and connect to the better signal of your saved networks. Hope that that helps.