Hi there, new to the forum.
I've just bought a GJ-15 from Thomann.de (good service btw, I recommend them). It plays pretty nicely but I have put a couple of pieces of thin folded cardboard under the bridge to raise the action by about 1mm as there was very very slight buzz in a couple of places. I've been playing a dreadnought with high action before so I've become quite fussy about even the slightest bit of buzz. I've moved the bridge forward slightly to improve the intonation (which is now very good up and down the neck, I've checked with my chromatic tuner and have been quite impressed) This means that the bridge is now not flush with the "moustaches" which doesn't bother me much as it's purely an aesthetic concern. I also cut a triangle of felt and put it under the part of the tailpiece which is on the soundboard. This has dampened the extraneous metallic noise somewhat but I'm wondering if there's anything else that I can do. Basically I find the sound a little too "wet", especially when playing rhythm softly. It is less noticeable when striking the strings hard.