The radios are NOT dual band, they are analog/digital. There are several reasons that they opted to do what they did. Those being: secured channels, roaming without constantly changing channels, GPS, just to name a few.
All of the radios that were in use before the switch over to the TRBO radios were 15-20 years old. The encryption boards were all failing and no longer produced. The mobile radios were also no longer supported and no parts were able to be obtained for them.
In regards to interop, since these radios are analog and digital, LE will still have interop with the whole county. Nothing will change there.
In regards to the antennae on the cars, the high-gain antennas and phantom antennas are no longer used. All vehicles are using 1/4 wave antennas. (S.O. anyway)
Oh, and don't get me started on the Motobridge. Not that it would work anyway as there are no towers nearby except the borders of the county.