MDJ reckons that double jointed bits are not great. Single joints are OK in her view, but double jointed bits can pull through enough that they may make the connecting link rub inside the corners of the mouth. I always thought French Links were milder too but maybe not?
I think Heather thinks that any kind of jointed pelhams are a bit dodgy though. We use a mullen mouth rugby pelham on one of ours and she likes that much more than any jointed bit we have tried.
I hope people still listen to their horses as well. Pinto doesn't have enough room in his mouth for a single jointed bit. All of the bits I've tried have been double jointed in some way. Currently his bit is very similar to a Myler, so not quite jointed, and not quite a mullen either.
His pelham is a mullen mouth, but it is "broken" in that each side can move/rotate independendly, but the bit doesn't collapse.