If you're not sure what to get or are a little uncomfortable with the assembly, I recommendg etting a Flightbox from these guys:
https://store.openflightsolutions.com/collections/flightbox-ads-b
If you get a single band, you're just getting weather because very few aircraft transmit on the weather frequency (978). If you get a dual band, you'll see all the traffic around you that is ADS-B out-equipped, and possibly a few others if you happen to be near an ADS-B equipped plane. But you still won't get a complete traffic picture, even after 2020 because there are aircraft that will never be ADS-B equipped.
I don't have a Flightbox myself (mine is homemade) but the guys that put it out are also some of the Stratux developers, so you're getting the best hardware and software because they provide support it after the sale. They also have additional features that is not in the mainstream release that the rest of us have, such as a very easy way to upgrade the software as new versions are released. So if you're not keen on the whole ordering/assembly process, they offer a 1-stop shop. I've also read where their support after the sale is top notch.