1) How far is a stride;
Ive been told about 20ft
Haha, i wish!
Whoever told you that has obviously got there numbers wrong somewhere.
2) is it worth it?
Unless you are extremely fit you won't be able to run more than a couple hundred metres without being exhausted. I know several people who bought these as a means of transport to work, but gave up on that idea pretty soon and just used them to have fun on.
You have to take into account that these things weigh about 5kg each, thats a lot of weight to be pulling around.
I'm not trying to put you off getting some but if you want to use them as an effecient way to get to work and back you will be sadly dissapointed.
Where abouts are you from, there may be people or a group local to you who could let you have a go on some before you order your own?
Hope this helps