I think the sti sway bar is hollow so it's not as rigid and strong as the solid bars like whiteline, avo and cusco. The tribeca front bar is hollow too, so even tho it's 25mm it will perform like a 22 or 23mm solid bar. But for the price, you can't beat it.
AVO is the only sway bar mount kit I've seen for the legacy and outback wagons.
The whiteline braces you speak of I think are for the Impreza wrx/sti platform.