The card you have there is probably the Action replay version or Action replay 2 version (it is if it has a little switch on the left in that pic). It can be used to input cheat codes as well.A youtube review in german...sorry
There some other versions around the world that do just what the other guys say.
What you say about the weight, is not really correct. The SNES cardridge has 50+ pins so the "fall off" thing is a bit difficult but actually there is a problem with the contacts. If you just touched lightly the snes or the construction on it, you get glitches or crashes and this more ofter if the adapter was plugged in and out often (older adapter).
To not have this problem, there was another famous adapter around without the cheat function called "Honeybee":
About the price, I would say it sells probably around 5-10$