I wonder whether this kind of notation is really relevant (changing metres every bar).
In his Sequenza VIII, Berio doesn’t use any, and that’s fine.
If it was solo violin like the Berio then maybe, but this is the solo part from a violin concerto - and to keep the orchestral players happy, this passage is notated and conducted in 4/4
OK. I understand.
Exactly! I’m no Doctor, so normally it’s just “Herr Professor” typically. 
On the few occasions I have used those, I got them to play back by using hidden tempo changes. One you have a couple of those, it becomes easier as you can copy/paste the signposts.