Are aero helmets worth it?

Aero helmets make a difference. I guess your actual question is: is an aero helmet right for you? Is it worth $90.00 to shave 30 seconds off your time and still place 45/80?

Or are you missing podium spots because the number 3 guy passed you on the bike and you couldn't catch him on the run?

 The shape of your head is more a factor than the size

Seriously though, many upgrades are trickle down tech from Professional level sports where seconds really do matter. For many of us the gains aren't worth the expense. Now a helmet is relatively cheap compared to a wheel set so If you got the coin go for it. Every time I think I "need" new wheels or whatever I look at some old race results and shave off the estimated time savings and I find that what I really need to do is knock a minute or 5 off my swim, or lower my run splits by 5 sec a mile and I more than make up for another bike gizmo. I will say I have been on a few long rides with a gnarly headwind wishing I had one o them fancy helmets

Best investment:  Training

Next best investment:  Losing Weight.

Now, that's all preachy....but compared to the common 'big ticket' investments (and this is a speed per dollar point of view), a good bike fit ranks first, clipless pedals second, aerobars third.

After those three, there is a precipitous dropoff in benefit...and an aero helmet is prolly 4th (depends on length of tri) and a good wetsuit is prolly 5th, with a number of other items competing for 6th and below...Aero wheels and frame, reduced size of aerodrink straw, bento boxes vs. underseat packs, carbon cages, aero shaped bottles, crazy drink holder systems, reduced bike weight, racing flats, yankz, etc. But they all rank behind the first three for the average triathlon. 

It gets a little subjective depending on your race (if it's hilly, bike weight matters more, aero helmet less, if it's a draft-legal race most of the aero stuff won't make much difference, etc).

Such as? 

There are few things that we NEED.  I think that has little to do with it.

For what it's worth, I can't think of many things to buy that save more time for the money invested than an aero helmet.

I am going to disagree with you a little Rick......Dollar for dollar in order 1) A good coach (this falls under training I suppose), 2) Aero bars, 3) Power Meter (this could also fall under training) 4) Aero Helmet, 5) Lighter Wheels.

A common misconception that is out there regarding weight is "why should I pay for a lighter set of wheels, when I can just lose a few lbs around the waist line?". The answer is that you are dealing with angular acceleration and momentum regarding wheels and not pure weight. Now that is not saying losing a few lbs will not make you faster, it will since speed is a function of power/weight ratio.

Now to answer the OP's question.... Aero helmets are great and you will get a benefit from one no matter where you place in the group. They are a good bang for your buck.  

Actually it's more like 12 mph... lemme see if I can find the source for that. I just read it. Might even be on BT already somewhere.

Define efficient.  You gain benefit from them at a much lower speed than that, and that's been shown repeatedly.

The notion that you have to be a certain speed to derive benefit is nonsense.

I still don't know what "efficient" is in this conversation.  We're not talking about an airplane wing here.  Aero helmets (and other equipment) produce less drag at very reasonable speeds.  Certainly less than the 21mph or whatever was claimed earlier.

Where does that mention that you have to go a certain speed to derive benefit from aero equipment?

If you're going to make a claim on a public discussion board, you can expect that to be challenged at times.  Don't get your panties in a wad.