well we have the 5620 - 22 channels and 38 codes or subchannels - with that many possible combinations you should be able to find a channel and code that are relatively free of chatter - they work ok - Practice with them before you go - get to know the tolerance of them.
Next time we go we will probably get two cell phones with a national calling plan.
But the radios work fine - they will not work if you are say at the Contemporary and you want to talk to someone deeper in the MK or over at Epcot. Inside th epark though they will have roughly a half mile range when you do not have line of site to the other person - depending on levels of interference you could get a mile out of them. The 2 mile or 5 mile rating that is stated on the package is a line of site rating. Either half watt setting or full watt setting I did not notice any appreciable difference.
We got ours for our last trip - could have retunred them but didn't - we can make use of them at our local amusement park - or local water park...