We use them, they are current limiter fuses and are designed to fit in a cutout the same as a fuse throttle. We use them to energize suspected damaged transformers, but haven't used them on URD risers. It was supposed to cut the time it took to install a Current Limiter Fuse and then remove the CLF after the transformer was test energized. When the ELF is closed you wait to soak the tr. then deenergize and install the correct fuse in the throttle. As a Troubleshooter I don't much care for picking up load and dropping it again but we now use the load buster for that. . .almost need a grocery cart full of gear up there to get the job done nowadays.
Both the CLF and ELF are made to have an interuption curve that will open faster and lower than the K-link or T-link fuses so the current never reaches catastrophic proportions before it clears. I've heard stories where the lead plug on the end of a CLF melted and red hot glass spewed out of it like flaming cotton candy. . .but that was just a secondhand story. Cool to see from afar. . .