We're still quite allowed to use expedient antennas... I can't see any need for permission or forgivemness... saw various designs a while back... been meaning to try to make one... might make for an interesting evening for the det...
They were only invented in the mid 90s or so, and I'm sure there's companies manufacturing a "tactical" version by now, just strikes me as odd they haven't proliferated further given the possible advantages... size being the major consideration...
I was under the impression they could be designed/used for any frequency, though not familiar with any performance tests, how they compare to traditional antennas in the lower bands we typically use... I know it's they've done wonders for cell phones...