Lots of walking ahead.

The family are off to Orlando for 2 weeks soon and we will be doing all the theme parks while we are there. I intend to get one of the step counters for while i am there to get a real idea of what i am burning while doing all the walking. A question i have to anyone that uses one is firstly what is a good one to get (im in the UK) and second if it works on movement what happens when im doing 50mph on one of the rides lol. The last question may sound daft but i have no idea how they work so all advice is very welcome.

CHeers
Iain