to answer your questions

1. check with the manufacturer of each bar as they are different. I know for sure that the new easton ec90 equip you have to use a 2 bolt clamp, but you CAN bolt on aero bars(alot of companies say thats a no-no).

2. There are a million different designs. I have 2, one I love and one I hate. I use the U.S.E. alien on my main bike, but hate the design because of the 2.5 mm bolts you use to tighten the clamp. They are very easy to strip, and I am always moving my seat. If you know exactly where you want your seat and never move it again than you wont have a problem with it. On my other bike I have a bontrager race x lite carbon post. It has one bolt built in to the side of the head, and extremely easy to adjust and only takes a couple of seconds. The only drawback is it is about 100 grams heavier than the alien.

That's about all the info i'm good for, hope it helps.

Mike