Is it a good idea to take out to ultrasonically clean and service 6G74 injectors?

The car runs fine (besides a poor idle) and economy is good.

Is there a chance the injectors can get damaged from this, or cause any kind of problems?

I ask as a friend is a mechanic and after doing him a favor he said he'd clean them for me. Just wondering whether there could be a drawback from doing this?

Depends on the equipment your friend has available.
A good setup will clean the injectors and check for leakage and flow rate. Nil risk of damage in theory, but you may need new "O" rings when you put them back.

On the other hand, if he is planning to use carby cleaner and a toothbrush . . . .

The draw back is you will have clean injectors, oh wait, that is a positive

The draw back is that if one or more are leaking they will then be found and replaced, oh wait again that is also a positive

Then there must be no negatives

It's a proper setup in a workshop that checks flow rates etc

Ok, seems like a good idea to do this then.
Madmagna, do you supply cleaned and tested injectors, in case it is found one is leaking or something?

Then there must be no negatives

But . . . .but . . . . all his "O" rings will disintegrate and need replacing!

Oh wait Mal can supply them too! (I'm guessing) lol

No I can't, the person cleaning the injectors should supply them