We use FileKicker for our downloads, with many different items so we can track different download locations and links on our sites. It lets us get some really good download statistics. I was comparing numbers...our average download completion for several programs is between 61% and 65%. And that's with our main tool being a download manager, which presumably people are using to download many of our files!
GetRight is a bit different...we have used our own tool GetRightToGo for all new user downloads for GetRight. We've been doing that for well over a year.
For GetRight, people first download the 300K small EXE build by GetRightToGo, which then when run it downloads the full 4 MB GetRight installer. (That 4MB is on the small end of when you'd ever want to use something like GetRightToGo--it makes even better sense with huge 100+ MB files; but we want to keep using and showing off our tools!)
I've always seen that both the tiny 300K file, as well as the installer it downloads got far higher completion rates than our regular links--the 300K gets over 91%, likely because it's so small and fast to download. And the EXE downloaded by it gets 85%. But there was always a bit of a drop between the two, people who downloaded the 300K file, but didn't run it (or possibly inflated by people who downloaded the 300K file twice.)
Comparing the worst case: the total number of download starts (completed + abandoned) for ToGo to the total number of completed downloads of the final installer EXE, it's still 68%. Not a huge amount higher than our regular downloads---but it is higher!
It is likely that for a bigger file, the difference would be even larger. Like some of the 1+GB games that have used GetRightToGo--many people would simply be unable to download the files without some assistance!