We did a construction job in Germany once with it......it was in a steep valley in the middle of a power plant, so high tension wires everywhere.
250 was not long enough, as we would have gotten too close to the wires....so a 500 ft line was used (nothing i would recommend)..
Then again, we used one in Congo, where we flew in geologists who wanted to explore a sink hole.......but that was only a short flight, picking them up on the line a few hundred meters away from the sink hole, then lowered them into it until they were safely on the ground...
In both cases, we used radios to get a feedback on distance above the ground........
But-again; i would not recommend anything longer than 250 ft.....or maybe its just me....