At a beginners stage, probably the most practical and acessible tension wrench is the home-made wiper insert wrench. When getting inserts, only get them from blades that are 16" or shorter. The longer blades have inserts that are more rigid not to mention thicker and wider. Take a piece roughly 4" long and hold it upright in a vise or with pliers. Then take another pair of pliers and clamp them about 1/2" from the bottom end and twist 90 degrees. Then bend the wrench down just below the twist to form an L shape.
This is a good wrench for a beginner and a pro and will give you good feel as well as showing you that there can be infinite possibilities to this one basic design.
All my best