I have had my blue linkia for two years now and he is still doing great. I had an orange linkia for a year, but the blue ring angel I had ripped it apart over night. Needless to say, I don't have that angel anymore. I found them easier than their reputation and IMO are worth the risk. You may lose one or two, but are only $20. Please don't try a grouper - I had a pretty blue-lined grouper, thinking he would play nice about a year and a half ago...he ate both my true percs.
As for sharks, I had a brown banded bamboo for about a year until he got too big for my 125. They need a 180 or larger to really thrive. Good tankmates for sharks are rays, groupers, moray eels, jacks, triggerfish, etc. Big angels will pick at their eyes and may not be good tankmates. I had mine with two tangs, tomato clown, niger trigger and a white-eyed moray eel. They are so cool, but really should be kept with minimal tank mates. They are, after all....sharks. They are the top of the food chain and if it will fit in their mouths...at some point and time will probably eat it.
-Dr Marco :sfish: