Okay, this is just my personal thinking experience on going from pencil jets to fan jets....
Firstly they finally arrived, as out of stock - fitting was easy and i put them into my dual trim super lite.
practiced on my house to see what i had let myself into... well you certianly know your cleaning with fan jets, the noise on the window really is loud !
Got good results so bit the bullet and did a whole day - standard cleans ( no new ones ) - WOW! left flow on same rate as i use for pencil's and after the second house of the day i was flying - rinsing was sooooo quick and easy. even one of my fav. regulars commented on how the water sound to be really hitting the glass and washing the frames clean.
by the end of the day i had used less water than normal ( approx 50 ltrs ) and finished over 40 minutes earlier than normal

The next day was all new cleans and again the fans removed all the built up grime mould and moss easily, however i did have the following - after rinse i noticed that there was some areas of 'grit' left behind - i have had this with pencil's but seemed worse than normal on 2 of these first cleans - so had to re do several windows again.
this maybe down to my technique or brush, as it's best to keep the brush on the glass with fan jets should i change to a flocked brush head that holds the dirt better ??
So with more practise and maybe a different brush head the fan jets are proving ( so far ) to be a good move.
and thanks goes to Peter fogwill for advise on another thread about fan jets.
Darran