Mike,
Material properties can very significantly depending upon the chosen aluminum alloy and tempering condition.
Here is a good overview on aluminum alloys which describe the different series (such as 1000, 2000, ... up to 7000 series) and the tempering designations (such as T2, T4, T6, etc.):
http://www.aircraftspruce.com/catalog/mepages/aluminfo.php
A good resource I use at work for material properties is here:
http://www.matweb.com/
Typically, you do get what you pay for. Sometimes marketing hype inflates the cost, but some brands are much stronger than others. For example, the Renthal Fat Bar uses 7010 T6 aluminum. This is a very high strength grade of aluminum. It is also shot peened for increased fatigue life.
I don't want to suggest that the Tusk bars are junk, since I don't know the specific aluminum alloy used. Just inspect them at a regular basis in the clamped regions. Aluminum will fatigue and fracture in a different manner than Steel. Aluminum is a more "brittle" material which fracture completely after a given life (sometimes unexpectedly). Whereas, steel is a more "ductile" material which will bend/deform before fracturing (giving you more of a warning).
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A general tip for everyone...
All aluminum handlebars should be changed after a severe crash or have ridden on them for several seasons (regardless of brand). Also, do not "rebend" aluminum bars if they get bent in a crash... it is not worth the risk.