I've had both, and don't notice any difference. I never had any black stuff dripping on my meat when I had my flat top smoker. If that were the case, wouldn't the same hold true for the UDS or any of the many cabinet style smokers?
Palmetto Smoke Company
Custom Pits Model A1 Offset Trailer, 18.5" WSM, 22.5" Weber Kettle, UDS Build in Progress