When you're trying for moat carp to get your Lu Shang's ( or for profit ) and you've broken what you had, kill these in the area for a few extra fish before heading back. The rods they drop can save you a trip back to town.
I fight these things all the time because the only things I can ever get them to drop for me, Lv: 15 THF, are Goblin Helms and Goblin Mail. I always have my signet on and never get and crystals. The only other thing I've gotten from them was a Clothespole once.
I use these for lvling @ 7-9 in E sarta barta, up at north most point. Ive gotten goblin mail (oncE), lots of lightning crystals, several helms and all fishing rods listed atleast twice. They drop lots of stuff.
These guys drop Lightning Crystals exclusively when you have Signet.
Also the higher level versions of these, they drop: Goblin Helm Goblin Mail
The low levels may drop the helm and mail as well, but I think the chances are very rare, it's more common for the lvl 10's to drop the pieces of armor.
I've also gotten these guys to drop Willow and Bamboo fishing rods. Once it even dropped a Fastwater Fishing Rod! I was amazed! :o I'm a thief but I don't even have "Treasure Hunter" skill yet.