Officially-licensed mobile adventure Harry Potter: Hogwarts Mystery launched last week to criticism of its hugely restrictive in-game energy limits.

The free-to-play app blocks you from completing in-progress missions unless you either pay up, or put down the game and then remember to come back within a certain time limit. One example foisted upon players within the first 20 minutes leaves your school-age avatar being strangled unless you cough up or wait it out.

Now, and perhaps in response to this controversy, Hogwarts Mystery is offering heavy discounts if you do want to pay for more in-game energy. Checking my app this afternoon, I can now buy 130 gems (which you use to buy energy) for just 99p, down from £4.99. The offer will apparently last just 48 hours.

But, oddly, others are being offered an alternative deal - the same 130 gems, but for 79p, and down from a different price - £2.99.

And still others do not see any deal offered to them at all, even when exhausting their energy limit and getting the usual prompt to buy more.

A/B testing - providing different options to different sets of people and seeing which is the most successful - of this type is not unusual, just as the game's energy model has been used in various other mobile games before it. But it's eye-opening to see what I would have paid for 130 gems (£4.99) was £2 higher than someone else.

And while A/B testing exists in many other smartphone games, the fact remains that Harry Potter: Hogwarts Mystery is an officially-licensed product backed by a massive publisher, based around a franchise associated with a certain expectation of quality, and - perhaps most of all - one aimed at kids.

I first heard about the app's A/B testing this afternoon from confused players comparing offers over in the US. There, players noticed 575 gems being offered at a discount, at both $4.99 and $9.99.

We've contacted publisher Warner Bros. Interactive for comment.