That's what I would've thought as well. A couple of friends who swore by it talked about the main pros as 1) parents have more control over what's being watched and how long, 2) minimize the risks of tablets getting dropped and needing to reach over to pick it back up for them, 3) not having tablets too close to the face if the kids are holding them. I have a couple of toddlers, so the pros make sense to me.
My kids in the back are 2 and 6, I can appreciate wanting to look out for them but in my case at least -
1.) My kids are already using youtube for kids app and their streaming accounts like netfix are all child accounts setup for content and parental controls so no problems there.
2.) Half the reason we wanted the van is so the wife can hop around and ride in the back with the kids when needed so no issues with dropping and if Im alone with them and you drop it and I cant reach it looks like youre waiting till dads next stop. This never really happens though since I bought the 2 year old a new mini with a grippy 3 handle case.
3. This concern I would say is legit. It's just one of those things you have to watch and govern as you see fit but if you find it easier to default to the idea of a "entertainment solution" in the back as opposed to them holding their own tablets this would lead to my next point.
When I saw the ridiculous cost of what Toyota wanted for that entertainment package and how crummy most of the reviews I saw on it were I just priced out my own. Now I don't know if you're looking at going through all this hassle of trading in just for mainly this one entertainment add-on but if so for the cost of what Toyota wants for that thing you can put together a solution on your own that is far, far nicer than what you get with the van.
Couple of dudes like this
Van Screens. Bigger, better quality, more features and the kids don't have to share. For less than the cost of what Toyota wants I can get something like that and still have plenty left over for nice accessories to make it all clean and look awesome. Oh and these don't block my frigging rear view when I'm trying to drive. Hell, if you want to get really cool with it.. for that same add-on cost I could buy a new Ipad Pro 12.9 inch and toss it on one of these
telescopic mounts. That just blows away the factory setup and you even came out of it with a new Ipad Pro you can detach when not driving.
Good luck with whatever you decide.