I dont use the univalve but i use the american rhino hose which even with hot water doesnt stretch anymore than when its cold. But you can also get the rhino hose specific for the uk univalve which is much stiffer and designed specific for the uni valve.
Personally I dont see the advantage of the valve compared to the tap in my set up.
If i didnt wrap the hose around me, then i can kinda see an advantage in not dragging a weighted tap valve at the end of the pole hose. But,,,, you would have to make sure you have plenty of pole hose dragged by your side for when your extending the pole. Unless im missing a trick here, that sounds like too much faff. Either having to whip the hose infront of you, or bending over and picking up your pole hose every time etc etc.
Where for me, once ive clipped my hose on, I walk and the hose n pole hose follows. No picking any hose up or making sure I have plenty near me for extending the pole. The tap is by my side like a gun slingers holster and its less than a couple of seconds to switch on or off. Compared to having to hold the pole a set way to make it easy to tug the pole hose at the base of the pole and as some of you are saying, its a couple of tugs sometimes. Whereas the tap works everytime.