You're right, it's spelled Contiki. I haven't done one my friend friend did. Basically they are prearranged tour like Globus and mainly for the under 35 crowd. My friend went on a European one. Sure she saw a lot of not any flexibility or free time. Imagine going to Rome, driving to the Coleseum, getting off the bus, taking a quick peek, then onto the bus to the next country! When when the brochure says, visit, you get off the bus, but in Belgium, she drove right through! Didn't even sample a chocolate
!!!
I think if you're a novice traveller and want to be told where to go, where to eat, etc, then try it out. Esp. if you are young, and going by yourself. But if you are going with a friend why not explore yourself? That's just my opinion because I'm not a tour type of person.