I've done plenty of jobs where you would have dozens of boxes in a straight run. 4squares aren't just for pull boxes, ya know. I also use them for light fixtures......
Long runs in corridors for lighting, fire alarm, etc. is another use.
But personally, I would never need such a tool. I put worms on the ends of all my fishtapes, and have no problems getting it to go through box after box. I don't have any pix of it, but I did 28 boxes in about 180' in a school once for either the fire alarm or speaker system (I don't recall any more) and pushed the tape from one end to the other. Pulled the cables from on end to the other, then went through and pulled loops into each box.