RE: the PVC;-
Ask the local planning officer whether there is any planning policy in place for replacement windows - there has been a huge move against PVC recently in planning circles.
RE: the Supplier;-
As with any product, the devil is in the details.
I'd only be taking delivery from someone whose work I had fully vetted and who had a nationwide reputation for good work.
You don't need to be part of some new company's trial-and-error product development and marketing strategy just because the price looks "right".
RE: the Windows;-
Triple glazing is expensive and you need a decent guarantee and proper fitting and follow up service.
In particular watch out for the window boards if the supplier is making good.
I have seen knotted and split boards being put into a house recently.
Builder had to take several boards out, replace and make good.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.