I embraced the Xtender technology quite a few years ago and outfitted both of my main basses(P and J) with the product. It performed beyond my expectations!
Having heard about the new DoubleStop retrofit lever, I was quick to both see the potential, and order two of them. I was not disappointed, and routinely use them during live sets with the several bands I am involved with!
Not having to lug around the 5 string, and being able to drop tune immediately and accurately to 2 steps is indeed priceless!