I do not know how much this will help because we have not had them very long but... my wife and I both have Polar CS200 that I got for us around Christmas. We have only been on a few rides outside and they have worked flawlessly. Now I have been using them on the trainer (has front speed sensor so no speed) and have had no problems what so ever. My wife and I ride together at home and there is no interference. The heart rate and cadence has worked great.
I rode this weekend and it rained for the last 30 minutes. The CS200 was fine and had no issues. I used it today while on the trainer and it was fine.
Ron