Serious question Phil.....
have you ever bought anything that has been good?
It's only that almost every time somebody posts up that they are thinking of buying something, you declare it's "rubbish"
Get a water bottle; localised heat is much more productive. You know the dangers, but what you may be unaware of, bivvys and brollys covered in dew or rain can't breath, sure have the bivvy open, personally I wouldn't risk it,