I'm still on the fence. I installed the ZRP lockout washers and have two days on them so far. My impression is that what you gain in stability and holding a straight, constant line in variable snow is offset by the fact that everything takes a little more effort. Gone is the "Summit feeling" mentioned above where you wiggle your hips a little and the sled turns. Surfing through meadows is a little less enjoyable. But you gain the ability to confidently point and shoot through narrow tree gaps.
Put another way, with T-Motion it seems like you always need to be on an edge; it doesn't like to be perfectly dead center. But it's very easy to fluidly transition edge to edge. With the lockout washers, the sled will stay dead center, but it takes more effort to transition edge to edge and you lose the smooth, surfy feel.
I'm going to give it a couple more days and then remove them to compare again with stock.
This is on a 19 Summit X 165x3 with (otherwise) stock suspension.