Those 0% financing offers only exist because interest rates are extremely low. I don't know about others but you know what else is low these days? The return on my index funds. If I invest those £800 now, I miss out on what, £8 over the course of a year? Compounding that makes very little difference at retirement age but for many of us, the mental overhead to manage these loans and the chance of taking on too much (interest rates will go up again) and making a mistake is just not worth it. Besides, if you BNPL you wouldn't want to park that money somewhere volatile anyway, an index fund, what if interest rates rise and you need that money all of a sudden but your index fund didn't gain anything. All of a sudden you lost money. Maybe I just don't get it, I'm happy to learn if there's a flaw in my thinking here.