Yes - Personal experience has shown me that, in particular "speedlights" (IE on-camera / battery powered flash guns) have very differing characteristics in 2 main ways:

• light spread and uniformity
• Colour and wavelength content

I have found that cheap (what i like to call Chinese eBay specials) tend to be inferior in both, as they are designed to a price, and use "a flash tube" as opposed to a specially designed tube filled with a special gas mix. So therefore have varying "histograms" (if you like) in the same way that fluorescent lighting lacks certain wavelengths.

Of course we must not forget that all speedlights / flash guns have BUILT-IN Light modifiers, so the design of the reflectors and fresnel lenses within make a huge difference to the spread and uniformity, especially in the zoom models.

The same can be said for studio flashes, although the light modifiers are usually detachable, so cant really be considered in this case.

DONT FORGET - White Balance CANNOT cure everything if the wavelength was missing in the first place, that "information" cannot be re-created. A prime example being near-monochromatic sodium street lighting - if you try to get rid of the orange cast via white balance, you will end up with a near B&W image.