I did this with the When they Cry Kai DVDs before they dropped the price. £14 voucher at the time for a £2 DVD was insane. It got me the Stranger of Paradise Final Fantasy game for £8 on PS5 after all was said and done.If anyone has any doubts about any of the titles in the sale, it might be worth seeing how much you can get for them in CeX (if you ever go near a store).
For example, they're currently offering £7 cash or £10 store credit for the Muv Luv BD collection - Bodacious Space Pirates is the same. Nurse Witch Komugi R will get you £3 cash or £5 credit.
If you buy something and end up not liking it, you'll probably get most of your money back (maybe £1 down) - or possibly make a profit on it.
Obviously this is useless if you've not got a CeX near you, but still...