I'm not an LAE, so haven't a vested interest - my club is the RAeS for most things and I've never joined a trade Onion (which I'll admit I regretted once).
I'd suggest that common membership of a Union IS IN THE CAA'S INTERESTS. Higher pay and professional standards, which tend to go with unionisation (to a point anyway) should, treated well, lead to better safety. Look at the BALPA safety work - very creditable.
Doesn't mean that they will do anything about it, but imho mass membership of ALAE would be a safety benefit, and therefore something that the CAA should push for.
G