I pretty much gave up on D.F. certainly at my local, LHR. Evidently, the fees charged by HAL (or whatever they call themsevles these days) are so high that the prices they need to charge are no longer good. Not to mention they only want to sell the maximum size of all products.
Last time through LHR, I pre-ordered some items. The main item I wanted they only reported as out of stock at the point of confirming the purchase. On departure, finding he pick-up point was difficult. We walked past it twice as it had no clear signpost.
Having been told it was pay on collection, I thought that they would swap a bag for payment. They opened the sealed plastic bag, scanned everything and then put them into a new plastic bag ...!!!
I shan't play that game again.