I bought it about 6 months ago and keep in it a fanny pack (yes, one of those ultra-non-cool mini-backpacks). The device weights about 2 or 3 pounds (fairly heavy), pumps out 2 mW of interference, and usually jams phones within about 20 feet (more on this later). Cell phone jammers are just too big to constantly lug around in a pants pocket and certainly are noticeable with the antennas sticking out.
That was the problem of the person on the bus. First he was keeping it in plain view. Second he did not hide the fact that he was jamming (in the video he looks at the cameraman he is jamming). The third mistake is that he was constantly keeping it on rather that on-wait 5 secs to burst-kill everything-off.
I'm very careful. I don't look at the person. I reach into my bag, turn it on, and then take out a package of tic-tacs candy and take one, chomp on it for about 5 or 10 seconds while listening to people say WTF around me and then put the tic-tacs back in the bag and shut off the jammer. Anyone looking at me (which is often) sees that I'm sneaking a snack.
My greatest fear is cell-jammer-detectors/trackers which are surprisingly cheap. However I doubt that someone with a tracker can isolate me in 10 second of surprise use. Given that the tracker have to move around holding the device looking at the signal indicators means that I doubt that one can sneak up to me.
I most often have to use it while waiting to check out in shopping centers. People talk talk talk on their phone and never consider the people around them, erupting to gales of laughter. Second most often is in traffic seeing the driver in the car beside me yakking away and not paying attention. Jamming in a car is more difficult and less range but it does still work well. Third most common is at work seeing people that should be WORKING aren't. All these people find that suddenly they don't have phone reception anymore. It usually takes a few applications of jamming but eventually people give up and get back to what they should be doing.
The devise I use says 5-20 meters, but my real-world estimate is 20-30 feet (6-10 meters). In my local wall-to-wall mega-store using the device at the checkout lines causes WTF's from about 5 lines away, and occasionally all the way to the entryway / cart-storage with people stopped dead in their tracks looking with puzzled looks at their phones.
Yes I do know that the legality of the device is problematic and I'm prepared to fight it in court if need be. I only once came close when I was speeding and got pulled over by the police. The officer looked my car over and while talking to me asked what was in the black bag on the passenger seat. I replied that I respectfully refuse to answer any further questions and will exercise my constitutional right to remain silent. The cop dropped being friendly and became all business (not hostile but very imposing). He then wanted to search my car. "No". He goes back to his car for a long time with my license. A second police car shows up and while one is talking to me, the other is looking at my car through every window with special attention to the zipped fanny pack. They walk off a bit to talk it over and eventually after about 30 minutes from being stopped they let me go with a large speeding ticket (no traffic warning for me). Probable cause and fruit of the poison tree for the win.
I'd like to get a car-powered one that is supposed to jam 3G, 4G, GPS up to 50m away but there is no way that could be concealed. I have little fear that I will be caught short of becoming over-confident and careless. In short I am going to continue using my device to thwart the terrible talkers and telephone abusers.