The Multi Terrains are designed for rough terrain such as grass and dirt tracks. They are a lot of fun but they can take some getting used to / practise and do give the skater a good workout.  The following videos may give you an idea of what the Multi Terrains are like:

https://www.youtube.com/watch?v=A7FnwaiezhU
https://www.youtube.com/watch?v=NrC4pteM2Nc
https://www.skorpion.com/videos/instructional-videos.html

The Quadline Street Skates have traditional 100mm inline wheels and require less effort than the Multi Terrains but still provide a good workout.  They are designed primarily for smooth surfaces such as roads, sidewalks and skate rinks.  Here are some videos showing the Quadline Street Skates:

http://www.youtube.com/watch?v=aYmRq2mU7H8&feature=c4-overview&list…
http://www.youtube.com/watch?v=5qPjSPiHyEo ? Not in English but gives you a good close up of the skates in actions.