Extractor Venting Question - Backdraught Damper for In-line?

[BobT36]

Upgrading my in-line extractor fan (ducted from ceiling in-take to soffit extract grille). A couple of questions:

1. If I'm using one of these with insulated flexible ducting to a soffit grille, do you think I need to bother with a backdraught damper flap like this in the duct? Anyone else get backdraughts into their bathroom when venting out of the soffit through an in-line fan like this?
I'll also be installing a PIV in the house so presume that will help push OUT air through the duct when it's off and prevent cold air coming in, due to the positive pressure.

2. I'll be installing a louvred vent grille on the soffit, like this. What way do you think the ends of the louvres should "point"? I saw a video that said they should point TOWARDS the house so you can't see up the vent, and that will also minimise draughts. Though I presume that's then dunking the extracted moisture right against the house wall. Or does it not make much difference once outside?
I saw another video where the louvres were mounted pointing "sideways".

I'll be capping off the couple of soffit vents within 1m either side of the extractor, to stop the moisture making it's way back up.

 

[Murdochcat]

I don’t think back draft devices should be fitted. ALL homes need ventilation, especially in bathrooms and shower rooms so an inline fan will allow the room to breath all the time

 

[jj4091]

1) No

2) Towards the house.