The Promethium Spur boots for the warlock are not working at this time. I was trying to test them out but about half of the functionality of the exotic does not work. You can do everything that it says except the last portion of its full description: "when your rift energy is full, final blows consume your rift energy and create a healing and empowering rift at the target's location". As you should be able to see in the video footage provided, rift energy is not consumed to spawn a rift at the location of a recently defeated target. No rift spawns at all, and no energy is consumed. Rifts do form on daybreak kills (as seen in the first portion of the linked video), so there is no issue there. All weapon kills do not consume rift energy to spawn rift at the dead enemy location. I swap weapons in the video to illustrate this point.