UTI's and D-mannose, did it help prevent them? powder or capsule?

I’ve seen D-mannose mentioned here as a preventive for UTI’s.

What has your experience been like? Has it helped prevent them?

Comes in powder and capsule. Which is preferred or easier/cheaper method?

web md has good info. Reviews seem very positive.

My wife buys powder and empty capsules, and then fills her own capsules. I understand it is cheaper that way.

She seems to think it works well.