The differences are a much smaller case, 2.5" instead of 3.5" HDD, USB 3.0, an external SATA port. The actual machine is very similar to the S2 to the degree that it uses the same firmware (and the same firmware as the Allure M3).
Both players can do Blu-Ray menus, both can play Blu-Ray from an external USB BD drive.
We should get some A1080s this week so when I have one, I will do some demo videos and better answer questions.
The price is very competitive compared to similar specification players..