The Avira Antivirus Web Protection works like an HTTP proxy and needs a cache to verify received data sequences.
After scanning, the cached data is forwarded with maximum speed to the Internet browser. The Avira Web Protection works very fast, the search process delays the download very small.
In purpose of caching data, the Web Protection works up to 50% progress with about half speed. Thereafter, he proceeds at full speed. Therefore, the estimated download time remains in most cases the same.
However, the short-delay delivery at the beginning arises a subjective impression that the speed is slower.
Out of the same mentioned reasons, speed measurements of test programs or websites provide inaccurate results.