While on the subject of clamps, I advise all to steer clear of one type of single-handed clamp. To be fair, I've not seen them around for a while which is all to the good but they still crop up as surplus stock from time to time. Even if they were free, I'd advise against them. Why? Read on...
The single-handed clamps or quick clamps such as this
are pretty good.
However, another design appeared a while back using a different approach. Instead of the solid bar of the one above, it had small serrations along the top like so
The clamping bit slotted into a serration and to release you twisted the rod rather than press the flat plate on the first one. The first downside is that you were limited to clamping in discrete steps rather than variable as in the first example. Not too much of a problem.
But the worst part of the design is that unless you always rotated the bar back to a square on position prior to clamping up again, you'd end up applying the clamping pressure on only a small part of that arc. Which gradually wears away the corner. So if you are clamping to the same point, it doesn't take long for you suddenly to find that the wee corner of the arc that you are applying your clamping pressure gives way with the sudden release of the handle crushing your fingers between it and the frame. Very very painful. DAMHIKT.
When these came out at Focus I tried to get Trading Standards interested but they couldn't be bothered.