Yeah you save enough gas to drive . . . what . . . a few thousand more miles during the life of the tire according to the ads. This assumes that there is no significant reduction in braking traction to cause you to crash when you really need to stop quickly.
Simple solution for the braking worry: Buy at Town Fair Tire or another tire seller that has a money back guarantee.
Many years ago in another life I bought high performance tires from Town Fair and they did not make a single mph of difference on my favorite exit ramp. I returned them and bought a different brand recommended by them, same result...the car just wasn't going to do any better. So I returned those and bought long treadwear tires instead. I didn't pay a single cent more than if I had just bought the long treadwear tires first, despite putting about 5,000 miles on returned tires.
I think Michelin claims a 7% reduction in rolling resistance by switching to their Energy tires (compared to a standard radial tire). And I think I've heard elsewhere on this forum that RR is about 15% of total energy consumption, so if you multiply 0.15 * 0.07, that will give you your savings.
p.s.: It might not sound like much but Michelin also claims that over the lifetime of the tire, that difference will pay for the tire. I haven't calculated that out to verify...