The flex on mine was in the whole plastic head. There seemed to be an earlier version (that got 10/10) with a metal head looking at the pictures but the one I got was all black plastic and flexed when holding my bike by the seat tube. When doing any work on the drivetrain the bike bobbed up and down and the head creaked. Maybe I had one that was moulded poorly though.
I ended up with a Lidl one to make do which I found much more sturdy but the screw only clamps causes me problems with my hand (damaged tendons) so i have a Feedback sports one on the way. The lidl one is really stable but 4 legs is not so good on uneven ground.
For £50 the Ribble et al one is a really slick working stand and if I could clamp my bike by the top tube I would have been happy with it.
The PCS10 for £90 is an absolute bargain as it is so solid. Definitely worth it over the PCS9 as the clamp is better and it folds up easier from the looks of it (not tried to fold it). If I didn’t have the feedback I would go for the PCS10.