From the reading I have done on extension tubes, I understand that some are just 'dumb' tubes while others have electronics that may allow for metering and autofocus to still work. Further, from this question I gather that not all manufacturers or extension tubes are created equal.
What should I look for when shopping for an extension tube set?
Does Pentax sell their own or officially support a certain brand?
Are there certain known manufactures to look out for?
How big a difference is there really between a cheap extension tube set and an expensive one?
Does autofocus really work with 'smart' extension tubes?
Does it make a difference (for the auto features) what lens is being used?
Are electronic extension tubes even worth it, or should I just put the money toward a macro lens?