As for the 1090, it is really not needed if you fly under FL18. It's kinda become a marketing ploy.
Technically, if you are using a transmitter, 978UAT or 1090ES, you are requesting a traffic "Service Volume" for your position from the ADS-B ground station. In that service volume data from the ground station, you should get Mode C, S, 978 and 1090 traffic.
Having a Dual Band receiver would really only be of benefit for receiving 1090 Air-to-Air, or basically when you are not in range of an ADS-B station or above FL18. I personally use the AHRS model, and see Mode C, Mode S, 978 and 1090 traffic when I am in range of the ADS-B station, which most of my flying is in ADS-B coverage.
The 1090 might add some extra coverage, but most of the time you should be in range as the system is being built out pretty nicely by now.
Feel free to call me at 888-200-5129, and we can discuss some more if you want.