Most people that use them have their favorites, so be open minded and research them if you plan to buy any but the most inexpensive. A good source of information is the alt.radio.family newsgroup. There are many places either in retail stores or online to buy them at good prices. I have purchased all but the Rangers online. Whatever you decide to use while in the world, use it courteously.
Nobody likes to have a show interrupted by a squawking radio.
This applies to pagers and cell phones also. If you cannot set it to vibrate mode, turn it off in any quiet show. This is simply an earphone type speaker that may or may not have a microphone attached on the cord. You can use them whenever you do not want other people to hear the radio conversation. The ones I use have a microphone attached to the cord that can be clipped on a shirt or jacket and you can then leave the radio on your belt or in a pocket.