"I bought two of these for an install in a stud wall as these were the only 5m cables in stock at my local Screwfix branch as I didn't have the time to wait for delivery (plasterer was on his way).
They look and feel like a decent quality cable for the money (although if yet to actually use them).
A "flat" cable sounds like an excellent idea, but I suggest you think carefully before you go for one. Presumably people going for these are thinking of installing under a carpet or similar. You need to remember that it doesn't stay flat when going around corners or bends to left or right (up and down it does - along floor and then up a wall for example.
I'd recommend sticking with round ones unless you have a straight run. But at 5m, anyone with a straight run like that in their house probably won't be doing it themselves!"