Put it this way - they won't mix with Copplestone FW figures very comfortably. Not that I have seen them side by side - and I'm talking here about the riot cops, not the rioters which I haven't seen. But I have the full Copplestone FW range, and when I picked up the Offensive riot cops, my immediate reaction was - beautiful, but tiny. It's about stature as much as height. I agree with Karl, they're much more in natural proportion than the bulky 28mm figures we're all used to - but it does make them look 'smaller'.
Not everyone is bothered by these things, of course. But to me, the visual aspect is important, and I like figures to look compatible in size, stature and 'look'.