I'm not sure where all the ventile love comes from.
I think it's actively dangerous. If you're in sustained rain or crawling, with persistent wind and temperatures below about 10C, it will chill you like nothing else. And you will get wet - very wet - in the end.
I had one nasty brush with hypothermia with that stuff, and would strongly advise against it if you're planning to use it for extended periods somewhere like the Highlands.
Summer use, or short periods on low ground or in sheltered areas, or use on days where the temperature is guaranteed to stay below freezing, then great. Otherwise - just no.