I recently tried a set of Profile Carbon Stryke aero bars on my older steel road bike. Not bad. I can see why some folks like them, especially for longer rides or stiff headwinds. Much more comfortable -- or, rather, less uncomfortable -- than the first or second generation Scott aero bars I tried a year or so ago. Never could get used to those. The main difference is where the forearms contact the arm rest. With the Scott aero bars the arm rests were in the middle of my forearms -- that was torture. With the Profile bars the rests were closer to my elbow. Not a perfect fit but closer.
Main problem was the aero bars made the cockpit cramped on my standard drop bars. I'd need an accessory bar to mount my other stuff -- lights, etc. And wider drop bars, or flared in the drops. With my 40cm wide drop bar there was no room on the top of the bar for my hands -- best I could do was hold the arced section between the tops and hoods, with my elbows flared out.
I can see why most TT/tri bikes use bullhorns, although those would limit hand positions for non-competitive use. But time trials and triathlons are a whole nuther beast. If the rider isn't in the aero bars most of the ride he's not going to be competitive against riders who have their fit nailed and can stay in the aero tuck longer.
Another issue is saddle adjustment -- especially height. If I set the saddle to the best height for getting in the aero tuck, it was too high for the regular riding position. If I set the saddle height to be appropriate for riding the hoods, tops or drops, it was too low for the aero bar and my torso wasn't open enough. My quads tired more easily... everything felt a little off.
There's a cleverly designed seat post/saddle rail that can be adjusted without stopping to accommodate both positions -- conventional bar positions and aero tuck.