how much of load the heavy-duty grip clip is rated for vs. the general-purpose grip clip (I plan to use it with at most two layers of woven ripstop film). If I use a general-purpose clip and it fails (weather too severe), how would it fail?
The difference is in how much material they grip. The HD grips about twice as much as the GP. So when your tarp is loaded, the HD will be less likely to rip out the tarp. It is the tarp the usually fails not the clip. I would recommend the HD where you can only grip at a few places on a large tarp.