Pros: It works!!!
Oh yes, it works; big fun! :)
After testing with my own phone, I put it in my pocket and went shopping at the local supermarket -- always a good place to find a dozen people chattering away about nothing in particular.
In a clear space this knocked out some phones as far as 30 feet away. Within 15-20 feet it took out most of them.
While it doesn't take out /all/ cells in that range, even the ones that still get through pickup so much interference that people hang up and try to find a "better" location.
Works through walls and store counters and displays. Great fun to walk up the aisle /next/ to the aisle with the person with the phone, and listen to them try to figure out why their signal died.

Cons: Mostly minor--what others have said. Antennas are a bit fracile, so treat them with care. Silicone-glue a rubber grommmet around the on/off siwtch to prevent accidental turn-on. And probably not a bad idea to replace the battery with a higher-quality one.
To this extent, you get what you pay for.
But hey, IT WORKS, and for under $40/American you can't go wrong.

Other Thoughts: One other thing would make this a perfect device -- if they actually made it /look/ like a cell phone.
But keep it in your pocket, and no problems.

Bottomline: I -love-this device! Yeah, you can get more powerful jammers with a wider range, but you'll also pay 3-6 times as much. This one does exactly what I want: clears a zone around me in which the yackers have to either stop yacking, or move.
Best $40 I ever spent!

Pros: Very small and easy to use !
Just turn on and get rid of talkative people
Work very well in France, it depends on the mobile you want to block. 75% blocked !

Cons: No adapter for France to charge it, I just bought one for 3 euros
How to fill up 500 characters for the review with so little constraint

Other Thoughts: Don't expect to get through big walls. Very useful to end quickly my neighbour's boring conversation. Works also in street while walking.

Bottomline: Very compact and very cheap ! Shipped as long as written on the site... 12 days for me !

Pros: shuts down the networks in my room
you can have looaaddddsss of fun with it
awesom for teasing your friends
and also very easy to use

Cons: doesnt work all that well on 3G
but if i can tune it (with some help) it will probably work great
switch does indeed press to easily

Other Thoughts: im having loads of fun and i dont even have it that long
just for the price its awsome
i might buy a stronger one as soon as i have more money at hand

Bottomline: just buy it, if you can figure out how to tune it its great.
and if you have some money lying arround its just worth it.

Pros: It's very compact, I keep it in my pocket.
It charges on AC 240v (european country) and with a car adaptor.
It's work very well in France when gsm are close enough.

Cons: It require a few seconds/minutes to cut the signal.
Sometime the signal blocker is 1 meter close to the phone but the conversation is still going on.
On/off button can by easily pressed by accident.
Antennas seem to be fragile

Other Thoughts: It's very usefull when people are phoning in the car.
The last time I use it, my father was driving on the highway and phoning at the same time!

Bottomline: I will by a new powerfull one. It's funny to make the people crazy!
It's very cheap, particularly when you pay in €uro ^^