Can a design registration stop a non-identical product?
If you register your design, you will be able to stop the sale of products which are not just identical to your registered design, but also products which are "substantially similar in overall impression" to your design.
In assessing infringement, more weight has to be given to similarities than to differences between your registered design and the infringing product. You have to consider how similar the registered designs is to designs which have come before it (so called "prior art" designs). You have to pay particular attention to features identified as new and distinctive features in the design registration. You also have to consider the amount, quality and importance of features that are substantially similar. If those features are practically unavoidable, then those features will be given less weight in the consideration of infringement. The assessment of infringement should be made through the eyes of an "informed user" of your type of product.
The case of Hunter Pacific International v Martec Pty Ltd  FCA 796
shows how these considerations play out in the real world.
Hunter Pacific International is the owner of Australian certified design registration no. 340171 for the ceiling fan hub design shown below:
Martec Pty Ltd imported and sold the ceiling fan shown below under the brand name "Martec Razor":
Hunter sued Martec for design infringement.
The judge found that the informed user "should be taken to be a person who has an understanding of the manner and extent to which the design of a ceiling fan hub is dictated by function."
The judge noted that the differences between the Razor and the registered design include the flatness of the bottom surface of the lower motor covers, the shape of the cut-out apertures, the absence of any lower canopy in the design registration and the differently configured upper hub and the differences in the degree to which the upper surface of the lower motor covers slopes.
Nevertheless, the judge found that the informed user would perceive these differences as "minor, and as not having any significant impact on the overall visual impression conveyed by each of the two designs".
The judge paid particular attention to the similarities which would seen by an informed user when the when ceiling fan hub was installed in a ceiling.
The judge found that the Razor was substantially similar in overall impression to the Design Registration, from the perspective of the informed user, and therefore infringed the Design Registration.