Well it may be common, but I've never encountered it before.
The truth is that you just haven't been aware of it before.
It happens online, in print, on TV and radio. Even in direct mail. Anywhere where marketing people can put two different "messages" in front of parts of their audience, and test the result.
Some tests are focussed on a specific product, and whether you choose to buy or not. This could include offering you different ways to pay.
Some tests are focussed on a variety of choices presented to you... to see which choice you pick out of the group presented (and to see if varying the group of offers makes any difference).
Some tests are just focussed on the overall impact to traffic (eg vistors to websites, or footfall in physical shops).
1) Is it also common for one or more versions of the website to completely omit any path to certain products? Specifically those with a lower overall profit margin? Not even a clue to their existence? Understandable with trial flavours of KitKat, but broadband?
Marketers know that offering choice can be a problem: confused customers don't buy.
So offering a choice can be good for some customers, but bad for others. Which is best for the company overall? Should a choice be removed? Or offered in a totally different way?
Therefore tests to show the impact of completely removing a choice are perfectly valid propositions.
2) If I went to a site a few times to check certain aspects against a competitor I was considering, and found not only a different view sometimes but information I knew I had seen shortly before was no longer there, I would run a mile from such apparent incompetence.
Valid point. Offline adverts do this by varying (for example) in different TV regions, or on different radio stations.
Online testing requires the website to take care that you see a consistent behaviour across multiple visits. Cookies are a likely part of the solution.
Using different browsers, or different computers, makes it easy to see different variants - and some people will see this. But most won't (as you haven't, before today).
How difficult has it been to overcome a historic bad reputation, and how easily will this tactic destroy all that hard work? The tactic, nay - the strategy, needs immediate binning before it has the wrong effect.
That was my initial reaction, as an engineer, to seeing what marketers did. Now I understand it, and why it is done (selling is, in large part, psychological).
With understanding, I can temper my reaction to any one encounter, based on whether I think a company is doing something fundamentally wrong (such as omitting something in the advert (ala the ASA ruling).
In this case, what are PN actually doing wrong? They are failing to offer one of their product variants, in an easy-to-find way, to some of their website visitors. But they haven't made it unavailable to anyone, or discriminated in any way. Just made it hard to find.
Ultimately, the tests will determine what is the right way to offer the variants... whether that is on the home page, a product page, or the sign-up journey. Then PN will stick to the best way, and move on to test something else.
Isn't that better than having a marketer guess at which way works best, and sticking with that method come hell or high water?
Of course, there is a thin line here. If the tests show a departure from credibility, then more people will walk away because of a lack of trust, rather than just failing to like the offer enough to buy it.
I don't think the PN test here is enough to cause mistrust.