As a scientist allow me to shed some light on this confusing subject:

There are many spurious over hyped marketing claims made by haircare product manufacturers that are used to win over consumers, but are not properly tested scientifically. Makers of ionizers claim many things such as......

Twice the water removal, so therfore less heat damage,
Less frizz.
Sealing the cuticle.
Keeps water in hair shaft: shinier, smoother, softer, healthier looking hair.
Fuller hair sexier hair etc etc etc .

There is also a massive overuse of ceramic buzz words such as 'jewels', tormaline, and that ceramic component' in a hairdryer somehow makes your hair healthier??

Try googling actual scientific papers on this, mmm very had to find anything to substantiate them whatsoever.

Funny also how there are so many varied claims and not one solid message.

But as far as i can tell Ionizers just reduce some frizzing of the hair caused by static build up. This may be more apparent in low humidity climates.
The reduction in frizz may make your hair feel softer etc. It is HIGHLY unlikey that they will prevent any kind of hair damage from as your hair still sees the same temperture, power and time under the dryer. if your hair is damaged with ruffled cuticles then the ionizer could make this seem more effective.

If you tried to cook a piece of food with your ionic hairdryer do you think the food would be less browned or burnt with an ionizer - No of course not. The heat is the overriding factor - see below.

Ionizers negativley charge air molecules by adding extra electrons to the air atoms and molecules.

They do this using either a differences in charges of materials (such as the mineral tourmaline) that produce negative ions passivley (ie by not using any power or electricity).

Or, have internal electrical devices that create high voltage rather like the peizo sparker on a gas cigarette lighter.

Tourmailine is just another way of producing ions instead of the high volatge method mentioned way but the end result is exactly the same. Its the same if you by an ionizer for your house .

One site used the term 'crushed tourmaline jewels emit the highest concentration of ions. This is non factual and highly exagerated. Tourmaline is just a simple mineral that readily gives up extra electrons to the air atoms running past it. Its actually easier to create far more ions by the electrical sparker method as is electrically powered and not passive.

At the end of the day all these devices can only produce very small amounts of ions or if the ionizers are too powerful they will start to emit ozone gas of which there is a legal limit on domestic products. So these devices are of minimal power maybe a 1-3 watts.

Ionizers certainly do not improve the evaporation of water and speed up the drying process. Water requires a COLLOSAL amount of energy to evaporate it. That why your hairdryer needs to around as powerfull as an electric hob ring 1600- 2000 watts to be effective and still takes around 10-20 minuites!

Did you know Its takes 5 times as much energy to turn water into a gas (steam) than it does to boil the same amount of water to 100 degrees.
Its because water atoms must vibrate enough to break their bonds from which they are attached to each other and leave the surface.

So....... the ionizer device of 1 or 2 watts wont reduce the drying rate as its power is totally insignificant.

Ionizers seal in moisture? This is also highly debatable.

When you dry your hair it is most likely heated to around 100-160 degrees Celcius.

What will likely have a far greater effect is :

The humidity in the air at the time or after you dried the hair.
And how intensly you dry the hair. ie how ,how close, and how hot, you dry it.

Other debatable claims say ceramic components regulate heat better. this is not true either. What regulates heat is the amouynt of air traveling over the heater. Less air or a restricted airflow means its hotter so be careful.