We have a set of these radios and they were invaluable at WDW. If you buy a set, they come in two different types. The less expensive kind have 14 channels I think. If you get these, you will hear everyone else's conversation in the world.
The second kind has 14 channels, plus 38 subchannels for each of the 14 channels. With these, you can always find a subchannel that is not being used by others.
The batteries can get expensive too. We invested a little more and got a set that has rechargable batteries. They recharge in about 3 hours or so, and you don't have to keep buying new batteries.
These radios are great for the parks, especially if you are in a group and want to split up. This way, you can meet back without anyone getting lost.