Here's a link to Sinclair International's catalog and their torque wrenches.
I have both the torque screwdriver and the torque wrench from Sinclair, and have found them to do exactly what I needed them for.
To answer your question about whether two wrenches are needed, I found the answer to be yes. For scope rings and mounts, the torque should be in neighborhood of 20 inch pounds, while the action screws need to be somewhere around 60 to 70 inch pounds. While the wrench will go down to 20 inch pounds, I never like to use an instrument at the extreme limits of its adjustability. In addition, the screwdriver accepts hex drive bits, while the wrench is a 1/4 inch square drive.
Hope this helps.