These handleposts don't adjust in height. They are each a single piece (other than the clamp at top and hinge at bottom), making them stiff. The four on the left have a 2-bolt clamp which you can clamp the handlebar directly to. When there's just this handlepost + a handlebar, the flex is minimized. You can find these handleposts in a variety of lengths. You have to be careful when searching through images of them, because the QR-version can appear similar from certain vantagepoints.

You can get right-fold and left-fold versions of these handleposts. You can also easily remove the handlepost completely, just like a threadless stem. I don't have any experience trying to pack a bicycle.

Here's how I can fold my bicycle with drop-bars, when it has no rear-rack to get in the way. Separate the seatpost from the frame before the fold. After the fold, put it back in with the seat pointing to the side. This is highly dependent on your personal setup, so, your milage may vary.