Many photographers are upgrading their rig because the newest cameras can produce excellent images at very high ISO. This presents the allure of natural light photography, which may produce some excellent low light images, depending on the several conditions.
One should keep in mind that all pros know that to produce top quality images, it is best for the photographer to control and sculpt the light on the subject. It is frequently the case that natural lighting is not optimal relative to the subject. In some cases you may be able to move the subject so that the natural light works to your advantage, but in many instances, the natural light is just wrong. In many instances you could move the subject for optimizing the natural light, but then the background is not what you want.
The best example of the difficulty of natural light is midday overhead sunlight. This light is the most difficult to work with. Most images shot with midday direct overhead light look amateurish and washed out. If you get lucky and get overhead cloud cover, then midday light is almost ok, but still not optimal.
What about the magic hour? You might get lucky and get beautiful warm sunlight at the perfect angle for the subject and background. But it is more likely that the sun will not be cooperating.
Natural light sometimes works but when it is not optimal for the subject or set, you will need a flash to get the desired light control.
ALZO Digital offers a variety of TTL Nissin flashes.