In reply to HP:
> The son of a friend is quite interested in climbing. So far we've done bouldering and I've bottom roped him up some routes. Would it be safe for him to belay me if he's attached to a ground anchor? I was thinking of getting a grigri or equivalent for him. He's a pretty slight 10 yr old and i'm 6 foot 7 and 90Kg!
I don't know why but this problem regularly comes up with a 10YO, not older and not younger.
One obvious way to take the pressure off the belayer would be to put a twist, or 2 or 3 in the rope before starting off. It used to be quite common, especially outdoors, to set up a top rope and use this to teach kids, with caution. Walls now, I think, would baulk at such rope on rope action but if they use bell ringing for the younger kids (and just about every wall does) then that is far, far worse for their ropes.
I'm not sure why you would want to use an assisted braking device, in my experience the problem with these is that they need to be left open and the rope controlled by sliding the hand down the dead rope, an advanced technique, not suitable for beginners. I've seen more people dropped like that than any other method, because they couldn't hold the rope and just watched as their dad hit his arse on the floor.
The Smart and the MegaJul are 2 newer devices which allow you to open the lock whilst retaining 2 hands on the dead rope, much better. The Matik I haven't used but the problem with the Eddy was unlocking it after it had locked, not suitable for kids.
The Smart also has the additional feature of making it much harder to get skin caught in it, which is the other major cause of problems in my experience. The Smart can be used and functions as a tuber too, so retains the principal of teaching friction, rather than giving the impression of button pushing which you get with a grigri.