I doubt the actual effectiveness or usefulness of the system mattered much to the police department. Most likely this was used for one of two purposes: a) as mentioned above, parallel construction and b) an excuse to arrest people they wanted to arrest anyway, with the system as cover.
I don't see the parallel construction here. Parallel construction would have to involve use of material that should require a warrant, but one was never obtained. Just generating valuable leads that result in investigation that leads to a warrant isn't parallel construction.
