Does dipstick testing for UTIs work?

They tell you whether there is anything you need to have a look at. I don't know what the figures are, but what would make them useless would be a high level of false negative results - and I doubt that's the problem. I'd have thought you'd be far more likely to get false positives - bacteria and proteins getting into the urine sample from outside the person's actual urinary tract.

I'm not clear - are you thinking you relied on these tests too much?

PS - you might find this article helpful:

https://sykepleien.no/en/forskning/2017/01/can-we-trust-urine-dipsticks

I sure do recommend that people at least try D-Mannose. As an old RN I am really anti vitamins and supplements, but I swear by this to stop UTIs. I was getting more than four a year, they were heading into kidneys. Haven't had one in more than a decade. Stops bacteria from adhereing to bladder wall better than cranberry and not acidic.
Yes, the dip sticks will give you an idea when to see the doctor, but must be fresh and uncontaminated.