Pretty much, it's the heavier Hollowgram crank arm (Si is the budget version of the SiSL2), but with an adaptor to allow normal chainring to be fitted.
Meaning you can fit those one piece double chainset on it instead of the adaptor + FSA chainring, despite that, it is still pretty light at 540g.
Whats up with these new Si cranks?
are they just hollowgrams with differnt branding?