Lap vent query

[Caws]

Who has fitted lap vents to their felt?
I'm still battling condensation in the loft and these vents keep popping up on different threads.
Do they work?
How many do you need?
I read the link below which has real scare stories attached to these vents - are they a risk or is the site scaremongering because they're selling a different solution?

https://www.glidevale.com/uploads/9b36108ead3faa2df4933e194aefdef9.pdf

 

[plastic_peanut]

Try some, they are easy to fit and cheap. If it makes no difference remove them.