Are there significant differences between different brands/models of immersion blenders?
America's Test Kitchen published a review of eight models in the April 2010 issue of Cook's Country.

Their test covered several common tasks for an immersion blender:


Mayonnaise emulsification
Making soup
Whipping cream
Making smoothies with frozen ingredients
Making pesto


They evaluated the blenders on three criteria: performance, usability, and ease of cleaning. The only blender to perform at the highest level across all three, and the only to win their top honors of "highly recommended" is the Kalorik Sunny Morning Stick Mixer. 

The model that I use is the KitchenAid Hand Blender. I have never had a problem with it, and it was the only other model reviewed to be recommended. It was dinged a few points in the soup &amp; whipped cream tests. 

The remaining models were either recommended "with reservations", or outright not recommended. The reasons for these included:


No cup included. The cup is important for ensuring optimal mixing.
Battery powered
Having to hold two buttons to use
Ridiculously loud
Excessive vibrations
General discomfort &amp; fatigue
Poor performance with one or more of the food tasks. This was typically attributed to either a weak motor, or a poor blade cage design. A poorly designed cage can restrict the circulation of food resulting in portions being over blended.


None of the models  reviewed included a Sunbeam or Braun. However, the Cuisinart model was, and received the lowest marks of all.