Aerobars are certainly allowed in triathlons but are not allowed in UCI or most other sanctioned road races except in Time Trials. I think you just have your facts backwards.

Clip-on aerobars are very easy to take on and off if you are doing tri's and road races. Usually they come of in less than a minute.

As for aerodynamics, even with my poor form I get at least a 3-5 km/h advantage while using them.