You are wise to be cautious Franny. I chose that site, because it makes it clear that you are getting the trial version. Here is the Driver Genius main site where I got the trial and Professional versions myself http://www.driver-soft.com/INDEX.html
Also, if you are concerned about site security, you might consider this browser add-on http://www.mywot.com/
I'm assuming you have good anti-malware software already?