There is a great post in one of the IA threads that summarizes the differences and trade-offs very well. I could not find it, so here is what I remember. (I have an IA 16.)
- Higher grade of carbon in the IA 1 (lighter and stiffer)
- Integrated cockpit in the IA 1 (more aero, but harder to break down for travel)
- Integrated brakes in the IA 1 (more aero, but harder to adjust)
- If Devox is included, it is highly adjustable and very good
I could not figure out if the IA 1 frameset comes with the carbon Devox cockpit. (It is pictured with the cockpit on the Felt site.) If so, that is a huge price advantage that narrows the value gap between the two.
Edit: Found one of the posts: http://forum.slowtwitch.com/...ost=5914961#p5914961