As a player, I am wary of direct downloads, because as Dominique says, it seems to pop-up the download right away and sometimes you want to abort the download because your not 100% sure you want to download.
As an affiliate manager, I am wary of direct downloads because you often do not get the same, or as accurate reporting with a direct link as when players go through the process of visit the site, and clicking the download button. There are more players who abort mid-download, less impression-views, etc. Plus, letting the player see the certifications on the actual casino site are important to further strengthen their chances to deposit and play for real money.