I bought mine from http://www.chimneyballoon.com/ some years ago and it works very well. The design allows some ventilation but it certainly prevents 'chimney reversal' in the summer and sooty smells entering the house.
I found it necessary to use an extension pipe to allow me to easily inflate it when in position, but that will depend on the fire/chimney/flue design.
I've never known it to be noisy and I can't imagine how it could rustle in the wind when properly installed and inflated, as it will 'grip' the sides of the flue.
We have used the absolutely free solution of "black bin liner stuffed with loft insulation" in our spare bedroom chiney for several years now. it works fine. I wouldn't go to the expense of buying a balloon, especially as the bin liner cannot actually be seen, as it blends in well to the sooty chimney walls/opening.
Only downside to bin liner solution may be that it could make a bit of a mess when it is eventually pulled out of the chimney (whereas balloon could be deflated for purpose) - but nothing than an old sheet on the hearth couldn't handle!
I think there are two aspects to 'works fine'. The first requirement is to substantially block any chimney downdrafts during periods of non-use and there are clearly many ways of blocking up a chimney that will achieve this.
However, there is the second issue of maintaining adequate ventilation. An old duvet or stuffed plastic bag may not work very well in this respect, but the lack of ventilation won't cause any problems in the short term so it could possibly be concealing a problem that gradually grows over time. The type of chimney capping will also play a part in this respect as well.
I'm not overly concerned about ventilation in our chimneys because they are used every winter anyway, but it's something to consider when blocking up a chimney for the long term.
Can't see why a chimney which is capped would require a chimney balloon. If it's permanently blocked that's a different matter. I thought the idea of these things was to block a chimney not in use for the summer.
Stuffing a duvet or bag of paper (or even just paper, depends on the size of the flu) ) up the chimney for the summer should do no harm.
A bit of placcy drainpipe (often available from your local tip free) wedged alongside will provide ventilation.
My chimney balloon came with a little red warning notice designed to be placed in the grate. I suspect they've had customers report the same sort of experience :roll: