Does using an aero helmet with road bike (clip-on) in triathlon makes sense or its benefits will just be evident when riding a tri-bike?
I’m no aerodynamics engineer, but I would think an aero helmet would be beneficial on a road bike as well. The wind does not know what you’re riding.
It would depend on his position. If the tip of that helmet is up in the air, it could potentially cost more than it saves.
If riding solo, then yes, it will benefit. If in a group, likely less, however aero helmets are generally larger, heavier, less ventilated and can restrict visibility … all reasons not to wear them when on a road bike in a group.
Yes, I was thinking about using an aero helmet for olympic tri without draft in my road bike with clip-on.
I have just done sprint tris, how much time I will save with an aero helmet in oly tri?
For the purposes of rules there may be some legislation against the use of aero helmets in draft legal events. The pointy rear end may be perceived as a hazard if someone were to fall on it.
I guess all the other sharp protruding points from bicycles aren’t hazards if someone were to fall on those. Better outlaw the ground I hear that can be a hazard if you were to fall on it.
Does using an aero helmet with road bike (clip-on) in triathlon makes sense or its benefits will just be evident when riding a tri-bike?
What it will be evident in a road race if you wear one is that you will try to break away. It is like putting a sign on the back of your jersey that says “Be careful, I will try to break away”. 
I saw a photo of someone that looked like Arnie Baker breaking away on a road race wearing an aero helmet. I asked him if it was him and he confirmed this. Next weekend Sergio Jr. tried the trick in one of his first road races. He pulled the peloton at high speed from start to finish and was passed by a sprinter kid in the last 300 meters. Lesson learned. He never wore one again.
Sergio
It would depend on his position. If the tip of that helmet is up in the air, it could potentially cost more than it saves.
Actually, even with the tip of the helmet in the air, you gain some aerodynamics because it breaks the wind going over your back. It’s talked about in a ZippCast podcast interview with a guy from the MIT wind tunnel, I believe. It’s not all about frontal area.
Of course, I’m no expert, so I (and the wind tunnel guy) could be wrong.