I have an old Speed 10 (original Speed 1) with a 4-2-1 homemade mixer and it's a pretty excellent kite. It has never once overflown, even in gusty winds. Excellent upwind and light wind performance. I think slightly better low end grunt than a Speed2 12 (although neither kite really has any decent grunt in my opinion). It's a bit like driving a 5 speed car stuck in 4th gear, requiring a little finesse and patience to get going but delivering well once you get it going. The leading edge zips are far better in my opinion than any subsequent Flysurfer deflate system. Bridles are pretty horrible, snarly, tangly, snagging on any plants, fish bones, feathers or anything else they can find.
My Speed 10 is currently on vacation for the past three years because I have better kites to fly, but I will pull it out again one of these months for some nostalgic old time fun.
I wouldn't recommend the kite to most people because the bridle issues can serve up more frustration than anyone needs to put up with nowadays....and if someone bought one on my recommendation he would probably want to severely harm me after dealing with his first major hassle. That being said, I still think it's a pretty great kite for its time and is enjoyable to fly.