I haven't used one, but here's my take on it.

Crap.

Seriously - they show an image of someone reworking what looks like a graphics card with it. That's a quick way to kill it IMO.

Their selling point is the speed at which it heats up and cools down. That tells me that the tip has a very low heat capacity. They also tout the 800 degree temperature, and in the FAQ go on to say

Quote:
5. How hot does the material get?
Cold Heat tools may achieve temperature levels well over 1,000F, but the exact temperature can be controlled through proprietary means.

This tells me that the temperature is not user-adjustable. The 'proprietary means' are likely to be a preset PWM power scheme in conjunction with the surface area of the tip (which affects cooling rate), ie, this iron is constant power, and the temperature depends on that power and the thermal loading of the work.

What does all that mean?

It is very hard to judge exactly what temperature you are soldering at. If you hold the bit on a small part for a few seconds then you could end up heating the part to 800 or 1000 degrees Fahrenheit. And with the low thermal capacity of the bit, the iron might not be capable of putting enough heat into a large component to be able to form a good joint quickly.

Both of these situations are undesirable. The former is likely to exceed maximum temperature ratings and lead to dead components and lifted PCB tracks (too much heat kills the bonding between the copper and the substrate). The latter is likely to cause poor solder joints, and can cause other bad effects in some components (eg NiCd or NiMh cells, capacitors) when it takes so long to heat the lead of the component up to solder temperature that the rest of the component gets that hot too.

Add to that the fact that the iron is not static safe either, and you can see why it wouldn't be let near my empeg,

If you really want a handheld portable soldering iron, then I'd recommend a butane powered one such as Portasol. They too are constant power (as opposed to constant temperature), but at least that power is easily adjustable so that it can be tailored towards different thermal loadings. With practice it is possible to do quite fine work with it, although you still have to worry about static issues.

But a real temperature controlled iron easily beats that too.