I haven't heard a complaint from the drummers I know.
The whole idea is that they shouldn't stretch and as far as I know they don't. So the motion is transferred similar to a chain. They are slightly lighter but not enough to invoke a nerdy moment of inertia calculation. I doubt that you would feel like suddenly your feet double the playing speed or any difference at all.
But still I don't know why we should switch to straps. It is true that chains require some maintenance but they are very easy to replace (in terms of cost and availability etc.) . I don't think it is the case for straps.
Long story short, if there was a problem with them we would be hearing about them by now. Having said that they are still esoteric if compared to chain solutions.
To be sure, you can buy only the strap and replace the chain on your existing pedal with it, or find an old Gibraltar pedal with same play length and beat the hell out of it.