I have one of the first ones out that performs the same as the day I got it , I also have what I would call a 2nd gen one , its a pain in the arse even after a service , switch on is easy but shut off is dire !
I believe as Smudger pointed out a lot of it has to do with pressure , but my 2 act so different even though pressure doesn’t alter !
I think I will just go back to hose pinching when these 2 give up , the only water lost will be when the pole is going up which 90% of the time is 2 sections , no biggie!