A cable's a cable...
I picked up a couple of long cables. Think they were 1.5 or 2m though. Certainly nowhere near 4m.
On ebay they said genuine Apple (for whatever good that would do for the copper inside....), they work fine with no error messages and were about £3 each.
I've not had the problem where they don't work, but I don't use them for data- only charging.It's not though when it comes to Apple, it seems every other software update they make the devices not work with third party cables.
USB extension lead - they go up to 10m.