As I understand this
synthetic thing, and I've been researching just lately as I too am getting ready to flush my system, it's all about the "glycol" base that comprises brake fluid. You got your organic glycol base or your
synthetic base. More manufacturers are moving toward
synthetic glycol because it's easier to maintain tight control of the manufacturing process than it is with organic glycol. Other than the base, they are the same thing.
One thing I did come across was that metal cans preserve the brake fluid longer/better than plastic cans. That could be important if your storing the fluid on the shelf in the garage for another year or so. I haven't seen metal can's for a long time though...
I'm looking at 5.1 synthetic myself, which is NOT silicone. 5.1 fully compatible with DOT 3 or 4.