My TWC installer disabled the dual band feature explaining to me that the high band doe not cover as well as low band. I have an Arris TG1672G which I rent. I live in a 50s era ranch home with plaster over drywall walls. I have a second PC 70ft and three rooms away from the router. I am hesitant to buy something that may not work without an extender.
This is dumb, because if you CAN use the 5 GHz signal, you should. It's much less crowded. He is doing this to simply prevent a follow-up service call for people that don't understand the difference.
It also depends on the remote device. Unless it's a newer one, it's unlikely it supports 5 GHz.
But, if you find a dual-band device only works with 2.4 GHz, you can configure it to only connect via 2.4 GHz.