What's the difference between the Lokk Latch models?

There are 3 models of the Lokk Latch line of lockable gravity latches.  Actually there are 4 if you consider the Lokk Latch Round a separate model (it is really a part of the Residential Series 2 line).  The 3 models are the Residential Lokk Latch Series 2, Heavy Duty Lokk Latch Deluxe and the [...]