Boy, I'm going to give you some advice, shut the hell up... You are advising someone a boot that you have no idea what his foot looks like. SPKs do not elliminate shin bang, last season I got compression fractures in my heels, I used SPKs. So both your points are false, yes they do help reduce the chance of shin bang, but the flex really isn't progressive enough to elliminate it.
Telling someone to buy a small size and stretch into them also doesn't make too much sense, the kid should go and se a bootfitter and get fitted into a boot that fits him and not worry about image or reccomendations, the only bot for you/him is the boot that fits.
Now i now you're pretty new to site so don't be put off, but just know your stuff or do some research before giving advice on boots, they are the single most important bit of kit in skiing.