Interesting that when you read the web site it says installs in 15 minutes, but when you click on the instructions it says 20 to 30 minutes!
After reviewing the instructions I bet it would work for the Frontier as well. It only appears to go about half way across the tailgate on a full sized truck, so it may go about 2/3 the way across the Frontier tailgate. The other dimensions where you'd drill the holes are probably pretty much the same between the Titan and the Frontier. After all it is one size fits all for the full sized trucks!
Looks like a pretty easy install to me. Install time would depend on how fast you could get the tailgate off and back on again after drilling the holes. Looks like it would work on any stock tailgate. They even list the 04 Titan and those tailgates are really heavy!
Only problem I see is it could bend the metal around the holes over time. Have you called them to see if it will fit the Frontier?