The Spark Core was the predecessor of the Photon, and has been superseded by it as such. The Photon is better in all aspects, and should be preferred over the Core.
The Photon kit contains a Photon, so unless he wants at least two of them (which is very understandable if he does), you might not need to buy the 'lone' Photon. Then again, once he gets started, he'll most likely want more of them anyhow They're quite addictive
Let us know if you need more info, glad to help.