Rated 5 out of 5 stars
This is the best download manager I can find.
I had the size mismatch happen to me once. It was because the file said it was 3.9GB but it was only 3.6GB.
I found another source for the download and it worked fine. The file really was supposed to be 3.9GB. This may not be the source of others mismatches but it is worth checking when they get them. It might be as easy to solve as it was for me.
I also have no problem browsing the interweb while downloading. But I never download more than half-a-dozen at once (they finish downloading faster than I can add new ones).