Most people have had good experiences, a few have had poor experiences, a small number of those, complain of some really poor experiences, likewise a small number report exceptional service, way beyond their expectations.
I've always been really please with the service I've had. And they've defiantly gone "above and beyond" on numerous occasions.
That said, big though Westfield are in the kit industry, they ain't huge so short falls from their suppliers can have a serious knock on effect if they happen.
And some things just are the way they are. We joke and moan about kit contents shortages, you know, the odd missing bits! But then every forum I visit has exactly the same moans about "their" manufacturer, right up to and including Caterham!
As for what the backup is like, well I can only speak from my own experience. And for me it's always been superb. Two, instances in particular sum it up. The first was after my factory supplied, (one of the first batch) trackday silencer failed the radius test on the exhaust tip. The factory custom made me an insert that would fit into the existing pipe, with the correct size rolled edge on it, in time for me to take a retest three or four days later. (If I'd waited for a complete replacement silencer it would have been several weeks).
The second was when I ordered an aluminium ducting kit for the radiator. I needed it on and working prior to a Welsh weekend trip on one of the hottest weeks of that year. Between my original parts enquiry, and the actual order, the entire production batch of ten had been bought and was being dispatched to the Dutch race series. Gavin, knowing how urgent it was arranged a back up plan, should the next batch not arrive in time, whereby the on site metalwork/fabricator guy would make one up for me by hand. The ducting made it to me in time, and the weekend went without hitch.
Or there's the time I bought my roof last year, I'd originally arranged with Gav to collect from the factory once it was ready. It arrived in stock the week before last years Donington show, so Russ brought it over their for me to collect, sat in the trailer with the drift car, to save me the trip to the factory.