That's one of the nice things about my Savage guns, they have tang safeties as well. My first long hunting gun I got back in HS was a Mossberg 500c, which I used on deer for a lot of years. Then later, I used the the Moss. 835 Ulti Mag. Next came the Savage 220. All tang safety guns.Were I to have my wish, given preference coupled with what I'm most used to, every long gun made would have a tang safety. If your son is used to a 500 tang safety, I wouldn't deviate from it on a defensive shotgun. I would personally opt for another 500, and retain that familiarity.
I shoot 3 different shotguns, all with a safety in different locations. Tang, behind trigger guard, and in front of trigger guard. Fun to switch guns. But more than once, on the comparatively low pressure stakes of a rolling rabbit, I've reached for a safety that isn't there.
To me, with a defensive shotgun in mind? That's a rather sobering fact.