Brian, I have several of that style of clamps (by other manufacturers) in 24", 36" & 50" lengths. That style of clamp is really handy and we use them quite frequently in my shop.
Here is something that we do in my shop to make using these just a tad bit even easier:
Step 1. Determine the distance between the preferred side of your circular saw's "base" (up against said clamp) and your actual cut line.
Step 2. Rip a nice straight board that width - it must be thick enough that the saw doesn't "ride up on it". Label board accordingly.
Step 3. When you determine where you want to make a cut on your workpiece, put a mark at each end of the cut.
Step 4. Using one-handed clamps or C-Clamps temporarily affix new board to workpiece.
Step 5. Position Saw-guiding clamp up-against said board and clamp it in-place.
Step 6. Remove said board and make your cut! Note: for my circular saw that is used for sheet breakdowns, the board is 1.25" wide and 56" long.
I hope this helps you or some of the other readers...
Otis Guillebeau from Auburn, Georgia
OPG3 Tweak everything!