Looks like a generic helmet. No one will stop you from using it in a tri. I assume it has the certifications it needs, but I've also hever had a referee check mine so it probably doesn't matter.

Can't begin to estimate time savings:
1. Doubt anyone has tested the thing
2. The brand probably didn't spend money or time on aero testing if it sells for 50£
3. Savings compared to what helmet

But it will probably be seconds faster compared to a generic road helmet. Don't expect 5 minutes savings over 180km

I've handled this helmet quite a bit as some of my friends own it. Without branding on it, you would say it's a Kask Bambino. However, it's much heavier than that helmet. Since you will be riding a 180km in aero with it (that's the idea I hope ;) ), consider if the weight would bother you.

I've got one and get on with it well and worn it for a couple of Ironmans, including Lanzarote.
Its only 60g heavier than the Kask Bambino but £200 cheaper.
Has all the safety certifications on the inside

And do you think there is any advantage with carnac tt versus my giro agilis helmet?
If there is only 2min benedit over 180km course this is nothing for my expetcted time 12hours for ironman

Look at it from another perspective? How much do you think you will cycle faster with it? The mental part and "looking cool" also helps a lot! At least you did everything in your power to be as fast as possible.

I would say it's faster than your Giro - but impossible to quantify by how much.

I have one. I like wearing it. Speed gains are impossible to measure, but what is easy to measure is the number of the little steel plates that became unglued (for no usage- or storage-related reason) and fell off the visor, and the number of corresponding magnets that fell off the body of the helmet.

So, it’s n=1, but production quality has turned out to be pretty poor.

But yes, it’s legal in a European ironman. Also the ventilation is not that bad for a tt helmet. If you decide to buy it, I recommend you get two visors (shaded and unshaded) so that you can cannibalize parts from one to fix the other if you don’t have time to replace the helmet before your race. Fixing is straightforward but those little discs like to get lost.

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"FTP is a bit 2015, don't you think?" - Gustav Iden

As said above, this is a knock-off of the older Kask Bambino. I actually tested this helmet against a Selector, then a Tempor. Of course, helmet performances are highly dependent on your head's position but this'll give you an idea anyway...
With the Chung method, the Krono was 0.005 faster than my road helmet, 0.005 slower then a Giro Selector and 0.013 slower than a Tempor. You'd roughly gain 2'20 seconds over 180km at 28kmh with a Krono, compared with a normal road helmet (according to this calculator http://www.aeroweenie.com/calc.html).
Also consider the ventilation of the Krono, which is below par. For an IM, I'd personally opt for an aero road helmet. ;-)

Jpfischer...tenks a lot