[Gracias] "I find speed change is quite buggy. when ever I change the speed I get video Jittery"
You're seeing interlacing issues. Depending on the speed, FCP does a good or not so good job of speed changes. If you want perfect slo mo, fast speeds or ramped speeds, then Twixtor is the way to go.
Walter Biscardi, Jr.
Creative Genius, Biscardi Creative Media
http://www.biscardicreative.com
Now in Production, "The Rough Cut,"
http://www.theroughcutmovie.com
"I reject your reality and substitute my own!" - Adam Savage, Mythbusters