The Thunderbolt was a way better siren. You could pull a chopper motor on on a Tbolt without removing the horn or taking down the siren. Same thing goes for the rotator mechanism. With a Hurricane you had to remove the siren head, tear it apart, then put it back together again.
For an all steel siren the tbolt was easy to make. The sheetmetal was a simple box with bends that could be easily made, the horn was just 4 pieces of steel pre bent that were welded together at the seams. Early ones had hand welded horns done with a stick welder (big thick bead) while the later ones appear to have welds done with a wire feed welder. You could tell on an old horn were they ran used up the welding rod and switched to a new one.