Sam,
Old Pilot is correct. If you are most interested in traffic, a receiver only like the Dual 170 will leave you wanting more. It is great for Weather. And it will become much better for traffic once everyone has ADS-B out, including yourself.
I typically recommend a "receiver only" for pilots looking mostly for weather, whereas I recommend a transceiver for those most interested in traffic and then weather. If you are most interested in traffic, I suggest wait and save up to get a transceiver... you won't be disappointed. I hope this helps.