We own a stick (Huawei E173). We use the Internet from Kölbi. The stick does not connect to WCDMA, but only to HSPDA.
The USB stick only connects to WCDMA based on the signal it receives. If you are in a zone where the Internet signal is low then you will have a slow connection. This is based on the coverage of the carrier's network and technology. The USB stick is working fine, the problem is with your location.