I wouldn't install Klusons right away. Or ever, probably. Grovers are fine.
Here's a tip if you get the SG: have the store intonate it when you buy it. Reason: the design of the SG makes it susceptible to intonation issues on the G string.
However, this is NO big deal. If the bridge runs out of space to intonate the G string, they can flip the G string bridge saddle in the store to give it the extra notch of space needed, and it's fine. You can do it yourself, but it's best to have the store/shop do it, so it's perfect from the get-go.
Can't go wrong with either guitar, and your son will love you for it.
Any questions, don't hesitate to ask on here!