Clip-On Aero Bar Questions

[menglish6]

I'm thinking about getting a clip on aero-bar, but I have read that this results in really screwy geometry of your bike when you actually use them. Something like the seat needing to be angled forward a bit and such.

Can anyone tell me how big of a deal this is? What the modifications to adjustment would be that would make the aero-bars a better fit, and what effect those adjustments would have on your fit when you aren't using the aero-bar?

thanks