Shape wise these two mice have very little in common. The Behemoth mouse has a really wide body with a lot of bends and groves that are meant to guide your hands to a comfortable grip. The Eclipse is very different in that regard since it has an almost symmetric shade. This also means that it can be used by left handed people although they will lack thumb buttons in that case. The scrollwheels are somewhat similar in the amount of tactile feedback, but the Eclipse's is translucent and is used as an indicator as to which profile is loaded.
The underside of the Behemoth mouse has a small door that you can open up to insert the weigths. Both mice feature a profile button located underneath which is used to swap profiles on-the-fly. The location is some what troublesome because you need to flip the mouse on its back in order to access it.
The trim weight system resides at two very different places in these two mice. The Eclipse has a removable palm plate that allows you to access the weights whereas the Behemoth has a door underneath. The fact that the weights are placed much higher in the body of the Eclipse is not a good thing because it gives the mouse a higher center of gravity making it feel a wee bit less secure to maneuver around.
From this side you can clearly see the forced ergonomics of the Behemoth contra the open design of the Eclipse.
The thumbs button arrangement is a bit better on the Behemoth because you have two large buttons compared to the two slim ones on the Eclipse. Position wise the Behemoth's are likewise more ideal.
Cable wise the two mice are very different. The Behemoth features a sleeved cable where the Eclipse makes due with a normal cable. The Behemoth's cabe is slightly stiffer, but it can also be routed out through the side of the mouse which means that this might not be quite as big a problem.
In comparison to the Razer DeathAdder and the Microsoft IntelliMouse Explorer 3.0 the Behemoth is almost the same size and shape, however, given the nature of its design the Behemoth has a tendency not to be quite as comfortable as its two similarly designed competitors.
The Eclipse looks a bit like the old Diamondback mouse from Razer, although it has a wider body with a few more trim pieces. The design allows for left hand users to use it as well, but they will lack the comfort of thumb buttons.
The driver suites for both mice look pretty much identical with the only difference being the color scheme and number of buttons you can assign. The driver is less featured than what you would expect for a gaming mouse. For example a feature like zero acceleration control and other tweaks are not available. The only thing that makes it a gaming mouse driver is the fact that you can tweak polling rate, DPI, and create macros.