MIL eliminators

the tuners always seemed interesting to me but i dont understand what you can do with them or how you know what to do with them. If i bought a tuner i would want to try to make my car faster as well as eliminate the o2 sensors but dont know anything about tuning and dont want to mess up my car? Any/all info on the tuners would be great. Thanks

also has anyone else ever smoked a mil eliminator?

are diablo and sct the 2 big tuners?

ive been looking into them alittle, do you just hook it up, turn off the rear 02 sensors, dump in the 89,91, or 93 octane program and done?

Can you change the shift points in an auto to make it like you have a "shift kit", what do you change for that, shifting points for rpm, mph?? when i talked to sct they said there was a firmness adjust but couldnt really explain what that meant very well. They also said that you couldnt adjust for rpm only mph and the mph only took affect if the throttle was wide open.
it would seem like you would need to make the car shift at a higher rpm and have more firmness so that it squeeked when shifting, but i dont think i really dont know what im talking about.

ive been checking out the hand held tuners which can tell the computer not to look at the rear o2 sensors
on another forum people are saying the tuners come with "canned tunes" that are junk and not even worth putting into the car and that i should get buy a programmer from TPS or VMP that would have a much better tune put onto the programmer. Anyone have any knowledge of this or experience with these hand held programmers?
Are the canned tunes junk or have people bought the programmer, installed the canned tune and seen a difference in HP and/or gas milage?