I use neck WRAPS and leave them on almost 24/7 and feel that they can work well. You need to put them on fairly tight and you need to let the neck air out at least once a day.. I also use a throatlatch sweat under the neck wrap. I have one mare that is insulin resistant so she has a heavy crest and I think the neck sweats have helped quite a bit. For her, I will also use the plain neoprene ones that you can't leave on for long, but I will use the sweating gel, wrap her neck with plastic, put on the neoprene sweat and work her. You MUST wash the gel off the horse, the plastic and the neoprene if you use that method, but that can really help right before a show.
Our show horses are not stalled but are turned out together on dry lot and we leave the sweats on them for turnout too. And yes, sometimes they do get removed! Velcro is such fun to play with. But they stay on most of the time. I don't see much of a downside to using neck sweats except they are work and it IS possible to burn a neck if use them with plastic and are not real careful. I have never burned a neck but know it can happen.