No, I have no personal experience of cystitis, but do have a few general comments that may be useful........or may not.
You mention that you are pain free....that is unlike cystitis unless you have a type called interstitial cystitis and this can only be diagnosed by camera insertion into the bladder (cystoscopy)
If this is the case then it may well be difficult to treat.
There are no reputable clinical trials which would indicate that D-Mannose has any beneficial effect on recurrent cystitis...try it by all means..."any port in a storm."
Don't worry, as the infection that you have in your bladder is unlikely to spread to your kidneys as that would mean "the germs swimming against the tide" so to speak.....very difficult.
Good luck.