You all know what I mean... those BATF approved unwieldy trigger packs (hellfires, etc.) that at least one table sells at a gun show.

I am curious if first of all, any of them are worthwhile. I would like to fool with a pseudo auto if I can, but if these are a $80 bump fire attachment, I would just as soon waste my $ on something else. What kits work for ARs and how would you rate them (in terms of fun, functionality, and nec. modifications)? I have other assault rifles as do many of you, so feel free to add a critique of a slap-on made for another rifle AK, FN, HK etc.

Do not waste your money.  Full auto is seldom used by well trained troops who have it anyway.

Understood. If installing a halfway decent kit requires permenant/semi-permenant modification  then I wouldn't fool with one. I am not too concerned however about proper tactics in this case, just looking for a little fun. Most of the time will be spent on marksmanship but I figured a little distraction for under $100 couldn't hurt provided they are worth a damn.

Learn how to bump fire. Quick way to dump a mag [:D]

Have tried bump fire and can't get it to work.  Bought an "auto boost" and should have just thrown $20 in the trash.  Am now looking to buy an M16 and have the real thing.