Not sure why people think Sio offers more than Toutai. They are both first grade quality backs. Sio is faster and more agile, Toutai is more of a big, powerful winger. Both are ordinary defenders at times, because they're wingers. Both can have a shocker under the high ball, although Sio has improved a lot in that area he's still not exactly a vault. They can both score a try, 10 for Sio and 7 for Toutai. Toutai does a lot more work than Sio in terms of helping the forwards out. Sio has more experience and panics less when he does make an error, but Toutai will grow into that.
Ultimately, they're about the same level, so it depends if you want speed or power and BA seems to want Toutai's bigger, stronger frame. Possibly to complement what Radradra offers on the other side, and also because we are light in the pack with the injuries we have. Whatever the reason I rate both, but you can't pick both.