Pre-emergent is pre-emergent. The same argument is always out there, is liquid better than granular, etc, etc.
Your distribution of chemical is always better with a liquid, in my opinion. It also requires more calibrated equipment to apply liquids, it also is typically cheaper than a granular. Granular is easy to apply.
Personally, I use granular in beds most of the time, but sometimes I will tank mix surflan with Roundup to save the extra step and it allows me to see where I have been without using a marker.
The Lesco guy is trying to clean out the old stuff - really old stuff, LOL. Snapshot started as a DF formulation, combo of Gallery and Surflan. Within a few years they switched to a granular formulation of trifluralin and Gallery: cheaper to make and also could formulate as granular. Haven't seen DF for years, and even Dow does not list it on their website.
So if you want to try it (unless he has a ton of it, you won't get any more), I'd offer him to take it off his hands for 5¢. It's at least 8-10 years old. You might want to check with a Dow rep to find out if it is still going to be effective, too.