Agreed, but he wont know without checking if they are proper Toyota retrofit option (if that even exists) or some aftermarket load of crap. Definately would check, and definately would ask them to show you what it will look like after fitted!
TBH, Ive used lots of different reverse park systems and by FAR FAR the best is the ones which have a reversing camera; mostly on Nissan cars ive found. Its easily the best system and they rarely go wrong unlike reverse park sensors which are IMO flaky.
I suggest getting them fitted but put the beeper on the outside of the car.
That way, potential victims will at least know you're getting close!
Vans, coupes and saloons, yeah, they can be handy there ( van window too high to see ground obstacles and saloon/coupe type cars with bad rear visibility and arse sticking out.).