Is it actually true that cystex will cure an oncomming uti?

No: Cystex is a dietary supplement (look for fda disclaimer in small print). It appears to be a cranberry concentrate plus assorted ingredients that might prevent infection but can't cure it. Only antibiotics can cure (bacterial) infections. Phenazopyridine (aka Azo or Pyridium (phenazopyridine) etc) is an otc medication that can decrease UTI pain. Medications are fda approved & have proof of safety & effectiveness.