I'm not one that usually likes warhammer historical products that much, they are expensive and/or unsupported. But I do have them on my watch list and I have been interested in their Waterloo game, not least for having a great looking book, but paying 36£ + shipping for a book I can't see first isn't quite my thing.
But now they have a 50% sale on all items, and also a somewhat lower shipping fee, so if your have been thinking of getting a game or supplement from them this is the time to go get it.
They stated in their newsletter and on the page that this if "for a limited time" but fail to specify when this time will end, so probably it's not going to be around for so long, perhaps until they sell X amount of books or something. But I would recommend everyone to be a bit quick about it.
The other theory I have is that they are selling out everything they have and then removing the entire line, you never know when Games workshop is concerned.
But until we know more hop over to Warhammer Historical and grab something you had your eyes on.