The flat wire I've used is the
adhesive backed type from 21st century goods. It's not inexpensive (16 ft. for $12.50), but if you use it only for running up the wall to surrounds, you don't really need much. You can then connect the flat wire to regular wire to run to your receiver/amplifier with
flat wire connectors, two of which come with each 16 ft. pack.
You can paint the wire the same color as your walls, and it pretty nearly disappears. Looks great.
One warning. When you remove this wire it WILL peel off some paint. If you rent, I don't recommend this wire. If you own, and plan to have your speakers in the same place for a long time, then it's no big deal.
I have no experience with
DeCorp Flatwire.