Emgee, yep probably, but its pretty unusual that I need that much accuracy on length anyway. As mentioned above I use a DTI with the top slide for accuracy, longer lengths I use slips.
Nigel, nice idea! We ought to make more use of those I think. I thought about trying it like you have but with just a screw. I've fitted a couple of M6 hex head screws and washers in place of the cap screws so its much easier to clamp now, I might even use it!