Right, here we go.
OP said he wanted a new key but asked if the eBay kit would be a cheaper option than just buying one key.
He was advised against a kit full of unwanted tosh and keys that would prove expensive to become fully functional.
And I quote "It is still not a bad buy if someone has a broken lock because the key blades can be swopped. My point is it may not be the perfect solution but it depends on what your problem was to start." It was stated from the beginning the OP wanted a new key, not a new lock.
You argued Rewmers case for buying a genuine Land Rover key and made it appear to be the more inferior option, then did that very thing.
Rewmer said that when you buy a Land Rover key it will be coded to the vehicle and require syncing, there was no mention that it wouldn't need plugging in and would work from the get go as you have inferred.
To sum up, Rewmer advised that buying a Land Rover key was the better option, you yourself bought a Land Rover key therefore you must also believe this to be the better option. You have argued for the sake of arguing, it must be as simple as that?