I, personally, am not a fan of mecate sets on a snaffle bit. I know a lot of the big name trainers use them and promote them but I hate the way they make the bit feel in my hands. There is too much motion in them when the horse is traveling and I loose touch with their mouth. Plus, because one side is heavier due to the 'lead' portion of it, it makes the bit feel unbalanced to me. If I can feel the difference through the reins, I can only imagine what the horse feels in his mouth.
IMHO, I would only ever use a mecate on a bosal hackamore like it was designed. For my snaffle bits, I much prefer a nice pair of harness leather split reins.