Well it is more complicated unfortunitly then just throwing some bars on the road bike... I did that for 8 months but it took alot of tweaking to get everything right (now I have a dedicated TT bike). I would definitly recommend aero bars if the course is flat to rollers. On the hill climbing itts the change in posistion is not generally warrented.

A couple things to note, riding aero bars does not come overnight. It is a new posistion with lots of challenges in handing, etc. You use your leg muscles a little differently in the aero posistion. You also need to be aware of your hip angle and power generation.

How much fast will it make you?

Well timetrial.org states than in a 40k itt aerobars (clipons) can save you 2 - 4 minutes total time. That is assuming a basebar tt setup I believe but a road bike with the bars lowered, a fast forward seatpost, saddle moved forward, etc can reliaze simular gains. I think 1 minute is feasable with proper fitting.

Good luck!