I agree, mine is mounted to a piece of 3/4 inch plywood and I use 4 large "f" style welding clamps to clamp it to a concrete bench. It works very well for 22LR and mild 45 loads. If you were trying to test something like a 454 Casull, you would definitely want it clamped to something more rigid.Back in the late 70's early 80's I used our Club's Ransom rest extensively in a series of testing various pistols. The one key element we learned was the Ransom must be mounted on a secure solid base in order to obtain reliable results. We mounted ours on a heavy concrete block pedestal that had studs embedded in the concrete to attach the Ransom base.
The reason I mention this is that unless you have access to a very secure mount for this Ransom, don't waste your money or time trying to use it. Also, this rest requires various grip frames. If you try mounting it on a normal wooden bench found on most pistol ranges, the boards will flex and create vibration and skew the results inducing unpredictable dispersion. The heavy the caliber, the more error induced.
For general pistol and pistol ammo testing, a solid sandbag set up can work quite well. However, to eliminate all human error, nothing quite beats a properly mounted Ransom Rest to test the capability of pistol or ammo.