As Parksy says, opinion is divided but unproven either way. Lets be totally honest, they dont do any harm and if there is a slight chance of them helping, for me its worth the cash.
As caravanners, we willingly throw bucket loads of cash at any new thing that comes on the market, stuff that will probably be used once then thrown in the back of the garage, so why skimp on safety?
I'm first in line for supporting systems that support safety, provided there is tangible evidence of them actually doing what they claim, the problem for tyre bands there is no corroborated evidence, only the manufacturers advertising hype, which does not show a clear benefit by comparing their demonstrations withe same vehicles doing the same tings but without their bands fitted.
If these bands were as good as they would have us believe, they would be so important that they wold be fitted as standard to all vehicles.
When you consider the working conditions of tyres, those on a caravan are less stressed (but no less important) than those on your tow vehicle or day to day car, so if tyre bands are seen as so valuable for a caravan they should be even more beneficial for their tow vehicles, so why do caravanner's with tyre bands, not have them fitted to their cars? It should be a no brainer!
There is no substitute for good tyre management, and whilst it does not guarantee preventing a blow out, it goes long way towards it. Systems that monitor pressure and temperature of tyres are a real safety feature provided they are reliable, becasue sudden rapid tyre deflation is thankfully quite rare. Most problems are due to slower loss of pressure leading to increased tyre temperatures, or worn tyres not being replaced in a timely manner.
If and when there is real good scientific evidence that these bands do have a positive benefit for caravans, then Ill be happy to support them, but until that unequivocal evidence is presented, I can't see a practical reason to spend money on them.