If it's a chipped key, the duplicate is probably not going to start the car, but it should open any mechanical locks the original did.
I don't know any way to tell a duplicate key from an original, chipped or not, unless the duplicate is obviously cut from a generic blank. If you got a new key from a dealer, it will possibly be identical. I suppose though, for an 11 year old vehicle such as yours, the replacement part might be a generic part and might be different from the one you have.
I don't see why making a copy of a key to a vehicle you legally own would be illegal, but I'm in the US and I'm not a lawyer.
You can possibly get a replacement key from a source other than the vehicle manufacturer, but if it's a chipped key, it's possible it will have to be associated with your vehicle. The association process, if necessary, could require hardware an independent shop might not have, you might end up at a dealer. If no association process is necessary, the key (if chipped) will probably still need to be ordered for your VIN.