Tri Is a recommended item, All the stats are useful excluding the mana, And the sheen proc is nice as her base AD is high. Polar I think you may be right from a technical standpoint in that it is a stance change, and they don't proc sheen. But unlike all other stance changes Hers deals damage and is used more as an ability. It currently is confusing as there is nothing ingame to clearly point as to why it doesnt proc. Also Triforce currently feels lack luster, champs like Vi, can easily proc Sheen 4 times in a fight, while Rek can comfortably only do it twice, which makes it feel really useless