Most people's finger in the air estimates are hugely biased towards underestimating how much they spend. An AI budget app that has like 50% accuracy would probably still not be useful, but 90% accuracy is fine, and while I have not gone around trying to audit AI budget apps I suspect the accuracy for good products is even better than that.
If you're gonna go the extra mile and use an AI-powered system to be able to cross-check data more in depth than a run of the mill report from your bank, it means you want 100% accuracy, not 90%.